WO2017018659A1 - Hot-dip galvanized steel sheet and hot-dip galvannealed steel sheet with excellent shelf life and bake hardenability, and method for manufacturing same - Google Patents

Hot-dip galvanized steel sheet and hot-dip galvannealed steel sheet with excellent shelf life and bake hardenability, and method for manufacturing same Download PDF

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WO2017018659A1
WO2017018659A1 PCT/KR2016/006398 KR2016006398W WO2017018659A1 WO 2017018659 A1 WO2017018659 A1 WO 2017018659A1 KR 2016006398 W KR2016006398 W KR 2016006398W WO 2017018659 A1 WO2017018659 A1 WO 2017018659A1
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steel sheet
martensite
hot
less
phase
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PCT/KR2016/006398
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French (fr)
Korean (ko)
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WO2017018659A8 (en
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한상호
이제웅
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주식회사 포스코
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Priority claimed from KR1020160041648A external-priority patent/KR101795918B1/en
Application filed by 주식회사 포스코 filed Critical 주식회사 포스코
Priority to US15/743,490 priority Critical patent/US10907233B2/en
Priority to CN201680043417.3A priority patent/CN107849668B/en
Priority to EP16830692.6A priority patent/EP3327164B1/en
Priority to JP2018503140A priority patent/JP6619079B2/en
Publication of WO2017018659A1 publication Critical patent/WO2017018659A1/en
Publication of WO2017018659A8 publication Critical patent/WO2017018659A8/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
    • B32B15/013—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to a material for automotive exterior, more specifically, cold-rolled steel sheet that can be applied to the exterior panel panels for automobiles because there is no surface defects caused by aging even during long distance transportation because of excellent aging resistance and hardening hardening, It relates to a hot-dip galvanized steel sheet, an alloyed hot-dip galvanized steel sheet and a manufacturing method thereof.
  • the steel sheet In order to protect the surface of the vehicle from external impacts, the steel sheet has a high yield strength. This contributes to the dent resistance and light weight by using a steel sheet with high yield strength as much as possible in order to improve the dent resistance to prevent defects in the outer shell during driving.
  • BH steel sheet (baking hardened steel sheet) of tensile strength 340 MPa class has been mainly applied to automobile exterior panel panels requiring excellent dent resistance such as doors, trunk lids and fenders, and the importance of yield strength is recently evaluated by dent resistance evaluation. As it increases, it is designed to have more than 180MPa as the yield strength criterion and is applied to outer board. Therefore, in order to contribute more to the weight reduction due to the increase in yield strength, high-strength hardening hardened steel sheets of 210 MPa, 240 MPa, and 260 MPa grades have been developed and are being mass-produced.
  • BH resistance increases, aging resistance deteriorates.
  • Deterioration of aging resistance is the generation of aging due to long-term storage in the warehouse before long-distance transportation and parts processing, causing a surface defect that appears wrinkles on the surface of the outer plate after pressing has a number of problems as a hardening hardened steel sheet. Therefore, there is a demand for technology development that can produce a composite structure (ferrite + martensite) type BH steel sheet having excellent BH resistance and excellent aging resistance and hardly causing aging problems.
  • the composite hardening hardening type steel sheet exhibits excellent hardening hardening characteristics due to a movable potential around the martensite (M) phase formed in the tissue, but has excellent aging resistance.
  • M martensite
  • Patent Document 1 Japanese Patent Laid-Open No. 2010-0023025
  • the annealing hardening steel with excellent BH is manufactured by managing the heating rate at annealing rate of 3 °C / sec or less, but due to the too slow heating rate during annealing, not only economic effect is insufficient in actual mass production but especially, C content is 0.02 Yield strength is higher than 230MPa level at the level of%, which also causes high surface defects when machining parts.
  • Patent Document 2 Japanese Laid-Open Patent Publication No. 2012-0025591 manufactures a composite structure-type hardened hardened steel by controlling the P content to 0.015 to 0.05% for steel sheets having a C content of more than 0.015%. Is over 440MPa class and the yield strength is around 220MPa.It is difficult to replace the yield strength of the existing 340BH steel with 180MPa class.In addition, some bainite (B) phases have improved hole expandability, but this also provides high yield strength when forming parts. Due to this, there is a high possibility of surface defects.
  • Patent Document 3 Japanese Patent Laid-Open Publication No. 2009-035818 also includes some bainite in the steel structure in steel, which leads to an increase in yield strength relative to tensile strength, which may cause surface defect problems, and the Cr content exceeds 0.5%. Since Cr-based oxide is formed on the surface of the steel sheet, it is difficult to remove the scale during hot rolling, and thus it may contain a large number of surface defects as the outer sheet material, which has disadvantages in manufacturing the outer sheet steel having a beautiful surface.
  • the present invention is to overcome the limitations of the prior art described above, by optimizing the steel composition and the manufacturing process, the hot-dip galvanized steel sheet or alloyed melting suitable for steel sheet for automotive exterior plate having a yield strength of 170MPa or more excellent in hardening hardening resistance and aging characteristics
  • the purpose is to provide galvanized steel sheets.
  • an object of the present invention is to provide a method for producing the hot-dip galvanized steel sheet to the alloyed hot-dip galvanized steel sheet.
  • the steel sheet is in weight%, carbon (C): 0.002 ⁇ 0.012%, manganese (Mn): 1.6 ⁇ 2.7%, phosphorus (P): 0.03% or less (excluding 0%), sulfur (S): 0.01% Or less (excluding 0%), nitrogen (N): 0.01% or less (excluding 0%), aluminum (sol.Al): 0.02 to 0.06%, chromium (Cr): 1.0% or less (excluding 0%), It is composed of the balance of iron and unavoidable impurities, and satisfies the relationship of 1.3 ⁇ Mn (wt%) / (1.15 ⁇ Cr (wt%)) ⁇ 20.5, and Mneq defined by the following equation 1 is 1.9 ⁇ Mneq ⁇ Satisfies 3.9,
  • the steel microstructure consists of 95% or more of ferrite and the remaining hard second phase by area ratio
  • Martensite occupancy in the ferrite grain boundary defined by the following relation 2 is 90% or more
  • P shows martensite occupancy in the ferrite grain boundary
  • Pgb martensite occupancy area in the ferrite grain boundary
  • Pg shows the martensite occupancy area in the ferrite grain
  • the steel sheet may further include one or more of boron (B): 0.003% or less (excluding 0%) and molybdenum (Mo): 0.2% or less (excluding 0%).
  • the area of fine martensite having an average diameter of 1 ⁇ m or less is 2% or less (excluding 0%) of the martensite phase forming the second phase.
  • the steel sheet may have a yield strength of less than 210MPa and a yield ratio of less than 0.55 before temper rolling.
  • the present invention relates to an alloyed hot dip galvanized steel sheet having excellent aging resistance and baking hardening property by alloying the hot dip galvanized layer of the hot dip galvanized steel sheet.
  • the continuous annealed steel sheet was first cooled to an average cooling rate of 3 ° C./s or more to a temperature range of 630 ° C. to 670 ° C., and then immersed in a zinc plating bath to perform hot dip galvanizing, followed by a temperature of Ms-200 ° C. or lower. It relates to a method for producing a hot-dip galvanized steel sheet excellent in aging resistance and baking hardening resistance, including; step of secondary cooling at an average cooling rate of 4 °C / s or more.
  • the steel slab may further include at least one of boron (B): 0.003% or less (excluding 0%) and molybdenum (Mo): 0.2% or less (excluding 0%).
  • the steel microstructure consists of 95% or more of ferrite and the remaining hard second phase by area ratio
  • Martensite occupancy in the ferrite grain boundary defined by the above relationship 2 is 90% or more
  • the area of fine martensite having an average diameter of 1 m or less in the martensite phase forming the second phase is 2% or less (excluding 0%).
  • the present invention after the primary cooling, immersed in a zinc plating bath to perform hot dip galvanizing, followed by an alloying treatment in the temperature range of 460 ⁇ 610 °C, 4 °C / s or more to a temperature of Ms-200 °C or less
  • the present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet excellent in aging resistance and baking hardening, characterized by secondary cooling at an average cooling rate.
  • the present invention having the above-described configuration can provide a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet which can ensure excellent aging resistance and baking hardening at the same time, which is used for automobile exterior plates without the occurrence of aging defects during long distance transportation. There is a suitable effect.
  • 1 is a mean Mn concentration of wt% (a) on martensite (M) and the average Mn concentration on the ferrite within 1 ⁇ m around the martensite (M) at the 1 / 4t point of the steel sheet according to an embodiment of the present invention It is a graph showing the difference of wt% (b).
  • FIG. 2 is a graph showing a TEM tissue photograph in which a martensite (M) phase is formed around a ferrite (F) phase at a 1 / 4t point of the base steel sheet according to an embodiment of the present invention.
  • the present inventors have studied in depth to provide a steel sheet with excellent moldability by securing both aging resistance and hardening hardenability to be suitable for automotive exterior panels, composite steel sheet that satisfies the intended properties by optimizing the manufacturing conditions with alloy design It was confirmed that it can provide, and came to complete the present invention.
  • the cold-rolled steel sheet of the present invention or the steel sheet comprising the hot-dip galvanized steel to the alloyed hot-dip galvanized steel, in weight%, carbon (C): 0.002-0.012%, manganese (Mn): 1.6-2.7% , Phosphorus (P): 0.03% or less (excluding 0%), sulfur (S): 0.01% or less (excluding 0%), nitrogen (N): 0.01% or less (excluding 0%), aluminum (sol. Al): 0.02 to 0.06%, chromium (Cr): 1.0% or less (except 0%), including residual iron and unavoidable impurities.
  • the alloy component and the reason for limitation will be described in detail. At this time, unless otherwise specified, the content of each component means all by weight.
  • Carbon (C) is an important component in securing a second phase in the present invention to produce a steel sheet having a composite structure, which is an element that is advantageous for securing strength by forming martensite, which is one of the two phase structures.
  • martensite is more easily formed, which is advantageous for the production of composite tissue steel.
  • the content control is important for making an optimal composite steel. If the C content is too small, a sufficient area ratio of the second phase cannot be secured, and therefore, the composite hardened steel cannot be used to manufacture a bake hardened steel sheet having excellent aging resistance.
  • the C content is too high, it is advantageous for the formation of composite tissue steel, but the yield strength is increased to increase the occurrence of bending defects on the surface of the customer's parts, and it is not possible to obtain the composite tissue steel of 210 MPa or less before temper rolling.
  • the present invention by optimizing the C content as much as possible, it is an object to produce a hardening hardened composite steel having excellent aging resistance even at low C content. If the C content is less than 0.002%, the composite tissue steel cannot be obtained. If the C content is more than 0.012%, the composite tissue steel can be obtained, but the yield strength is increased, so that it is generally impossible to supply the hardened hardened steel having excellent surface properties. Therefore, in the present invention, it is preferable to limit the C content to 0.002 to 0.012% range, more preferably to 0.004 to 0.01% range.
  • Manganese (Mn) is an element that improves hardenability in a steel sheet having a composite structure, and is particularly important in forming martensite.
  • Existing solid solution strengthening steel is effective to increase strength due to the strengthening effect of solid solution, and precipitates S added unavoidably in steel with MnS, which plays an important role in suppressing plate breakage caused by S and high temperature embrittlement during hot rolling.
  • Mn-Band Mn oxide band
  • the content of Mn it is preferable to limit the content of Mn to 1.6 ⁇ 2.7%, more preferably to limit the Mn content to 2.0 ⁇ 2.4%.
  • Chromium (Cr) is a component having properties similar to those of Mn described above, and is an element added to improve the hardenability of steel and to secure high strength. Such Cr is effective in forming martensite, and forms coarse Cr-based carbides such as Cr 23 C 6 in the hot rolling process, thereby suppressing the yield point yield (YP-El) by precipitating the amount of solid solution C in the steel below an appropriate level. It is an advantageous element for the production of composite steel with low yield ratio. In addition, it is advantageous to manufacture composite tissue steel with high ductility by minimizing elongation drop compared to strength increase.
  • the Cr facilitates the formation of martensite through improving the hardenability, but if the content exceeds 1.0%, there is a problem of excessively increasing the martensite formation rate, resulting in a decrease in strength and elongation. Therefore, in the present invention, it is preferable to limit the content of Cr to 1.0% or less, and 0% is excluded in consideration of the amount inevitably added in production.
  • Phosphorus (P) in steel is the most favorable element to secure the strength without increasing the formability, but excessive addition greatly increases the possibility of brittle fracture, which increases the possibility of plate breakage of the slab during hot rolling. There is a problem of acting as an element that inhibits properties.
  • the content of P is limited to a maximum of 0.03%, but 0% is excluded in consideration of the inevitably added level.
  • S Sulfur
  • S in steel has a problem of increasing the possibility of generating red brittleness, it is preferable to control the content to 0.01% or less.
  • 0% is excluded in consideration of the inevitably added level during the manufacturing process.
  • N Nitrogen
  • N is an element inevitably added as an impurity element in steel. It is important to manage such N as low as possible, but for this purpose, there is a problem that the refining cost of the steel rises sharply, it is desirable to control the operating conditions within 0.01% of the possible range. However, 0% is excluded in consideration of the added level.
  • Acid soluble aluminum (sol.Al) is an element added to refine the particle size and deoxidation of the steel, and if the content is less than 0.02%, aluminum killed steel cannot be manufactured in a normal stable state. On the other hand, if the content exceeds 0.06%, it is advantageous to increase the strength due to the grain refinement effect, while the excessive formation of inclusions during steelmaking operation increases the possibility of surface defects on the hot-dip galvanized steel sheet and also increases the manufacturing cost. . Therefore, in the present invention, it is preferable to control the content of sol.Al to 0.02 to 0.06%.
  • other optional elements may include one or more of boron (B) and molybdenum (Mo), which may help to produce a composite tissue steel by slightly improving the hardenability.
  • B boron
  • Mo molybdenum
  • Boron (B) in steel is an element added in order to prevent secondary work brittleness by P addition.
  • the content of the boron (B) exceeds 0.003%, there is a problem that the elongation is lowered, so the content of the boron (B) is controlled to 0.003% or less, in which case 0% is inevitably added Exclude.
  • Molybdenum is an element that improves the hardenability in a steel sheet having a composite structure, in particular an important element in forming martensite.
  • Mo Molybdenum
  • Mo and B may be added at the same time, or Mo may be added alone. In this case, it is advantageous in terms of formability by forming uniform crystal grains during annealing. Therefore, in the present invention, it is preferable to limit the content of Mo to 0.2% or less.
  • the steel sheet of the present invention may include the balance Fe and other unavoidable impurities in addition to the above components.
  • the base steel sheet constituting the hot-dip galvanized steel sheet or the like of the present invention preferably maintains the relationship of 1.3 ⁇ Mn (wt%) / (1.15 ⁇ Cr (wt%)) ⁇ 20.5 in the relation between Mn and Cr, which are hardening elements. Do. When Cr content is higher than Mn, even if both elements have similar functions in terms of hardenability, excessive addition of Cr, an element that improves corrosion resistance, is problematic in removing pickling scale after hot rolling. .
  • the base steel sheet satisfies the relationship of 1.3 ⁇ Mn (wt%) / (1.15 ⁇ Cr (wt%)) ⁇ 20.5. If the value exceeds 20.5 in the relation of Mn (wt%) / (1.15 ⁇ Cr (wt%)), the surface quality of the shell cannot be secured. If the value is less than 1.3, the Mn content becomes relatively high and Mn in the tissue This is because a band is formed and surface defects and processing defects may occur.
  • the martensite (M) phase is not formed at all, which is not in accordance with the present invention. If the Mneq value exceeds 3.9, composite tissue steel may be made, but the addition of a large amount of alloying elements may lead to an increase in yield strength and tensile strength and may cause a decrease in elongation. In consideration of this, in the present invention, it is preferable to manage the Mneq value in the range of 1.9 to 3.9, more preferably in the range of 2.1 to 3.5.
  • the hot-dip galvanized steel sheet to the alloyed hot-dip galvanized steel sheet of the present invention that satisfies the above-described component composition, it is preferable to include the columnar ferrite and the balance martensite as a microstructure of the base steel sheet, and may include some bainite The amount of bainite is preferably minimized or absent as much as possible.
  • the base steel sheet constituting the hot-dip galvanized steel sheet of the present invention is preferably composed of a microstructure of 95% or more of ferrite and the remaining hard second phase in area% based on the total thickness (t).
  • the ferrite fraction when the ferrite fraction is less than 95%, it is advantageous to make the composite tissue steel by increasing the fraction of two phases relatively.
  • the ferrite fraction decreases, the yield strength and yield ratio increase, which also causes high surface bending defects during machining. Therefore, the ferrite fraction is preferably 95% or more.
  • the fraction of fine martensite having an average diameter of 1 ⁇ m or less in the hard second phase is 2% or less (excluding 0%) in area%.
  • M very fine martensite
  • the fraction of fine martensite having an average diameter of 1 ⁇ m or less in the second phase exceeds 2% as area%, the yield ratio increases and the yield strength also increases, thereby increasing the surface defects during processing. It is desirable to manage the ratio to 2% or less by area ratio.
  • the martensite occupancy ratio present in the ferrite grain boundary is 90% or more at the area% defined by the following [Relational Formula 2].
  • P shows martensite occupancy in the ferrite grain boundary
  • Pgb martensite occupancy area in the ferrite grain boundary
  • Pg shows the martensite occupancy area in the ferrite grain
  • Aging is not a problem because it is not locked with potentials around the site.
  • M martensite
  • F ferrite
  • the average Mn concentration wt% (a) of martensite (M) on the martensite (M) and the average Mn of the ferrite phase within 1 ⁇ m around the martensite (M) phase at the 1 / 4t point of the steel sheet according to the following [Equation 3]. It is preferable that the concentration wt% (b) difference is 0.3 wt% or more.
  • M the hardness of the martensite phase
  • the Mn content contained in the martensite phase must be higher than that of the surrounding ferrite phase. .
  • the higher the strength of the martensite phase the softer the nitriding of the surrounding ferrite phase is possible, and thus the steel sheet having a lower yield strength and yield ratio can be manufactured, and the hardened hardened steel having excellent aging characteristics can be manufactured.
  • the higher the strength of the martensite phase the higher the concentration (density) of the solid solution C in the martensite phase, so that the C in the martensite phase is easily diffused and transferred to the ferrite phase at an appropriate level of baking so as to improve the baking hardness.
  • Mn concentration analysis of each phase can be carried out by measuring the average value of 10 points in each phase by using an EDS analysis method using a TEM.
  • the yield strength is less than 210MPa before the temper rolling and the yield ratio (YS / TS) is 0.55 or less, yield strength and yield ratio cold rolled steel sheet, hot-dip galvanized steel sheet and alloying Hot dip galvanized steel sheet can be provided.
  • the present invention after preparing a steel slab having a steel composition as described above, it is reheated.
  • This reheating process is performed to perform the following hot rolling process smoothly and to sufficiently obtain the physical properties of the target steel sheet.
  • the present invention is not particularly limited to such reheating conditions, and may be normal conditions.
  • the reheating process may be performed at a temperature range of 1100 to 1300 ° C.
  • the present invention includes a step of winding the reheated steel slab at a temperature range of Ar 3 + 20 ° C. to 950 ° C., followed by winding at 450 to 700 ° C.
  • the reheated steel slab in the temperature range of Ar3 +20 °C ⁇ 950 °C defined by the following [Relationship 4].
  • finishing hot rolling it is advantageous in the austenitic single phase region essentially. This is because by performing finish rolling in the austenite single phase region, the uniformity in the tissue can be increased by more uniform deformation in the tissue basically composed of single phase grains. If the finish hot rolling temperature is less than Ar3 + 20 ° C, the ferrite + austenite two-phase rolling is likely to be high, which may result in material nonuniformity. On the other hand, if the temperature exceeds 950 ° C, the coil warping may occur during hot rolled cooling due to material unevenness due to the formation of abnormal coarse grains caused by high temperature rolling.
  • the finish hot rolled hot rolled plate is wound at 450 ⁇ 700 °C. If the coiling temperature is less than 450 °C excessive martensite or bainite is generated to cause an excessive increase in strength of the hot rolled steel sheet, there is a fear that problems such as shape defects due to the load during the subsequent cold rolling occurs. On the other hand, if the coiling temperature exceeds 700 °C, there is a problem that the surface thickening by elements that reduce the wettability of the molten zinc plating, such as Mn, B in the steel. Therefore, in consideration of this, it is preferable to control the winding temperature to 450 ⁇ 700 °C. Subsequently, the wound hot rolled sheet may be pickled under normal conditions.
  • the wound hot rolled steel sheet is cold rolled at a reduction ratio of 40 to 80%.
  • the cold rolling is preferably carried out at a reduction ratio of 40 to 80%, if the cold reduction ratio is less than 40%, it is not only difficult to secure the target thickness, but also difficult to correct the shape of the steel sheet, whereas 80% If it exceeds the crack is likely to occur in the steel sheet (edge), it is because there is a problem that brings the load of cold rolling.
  • a continuous annealing process is performed in the temperature range of 760 degreeC-850 degreeC.
  • the annealing temperature is basically a two-phase annealing, which differs in the final martensite content depending on the ferrite and austenite fractions in the two-phase annealing.
  • the annealing temperature is low, the austenite content is low, but the concentration of C in the austenite is high.
  • a high strength martensite phase is formed, so that the bake hardening characteristic is excellent during baking.
  • the annealing temperature is too high, the plate shape during the field production, such as the appearance of warpage and relatively coarse martensite phase is formed, it is impossible to produce the hardened hardened steel excellent in the aging resistance required in the present invention.
  • the annealing temperature is less than 760 ° C., the tensile strength is increased to a temperature that is too low, not only to lower the elongation, but also to increase the possibility of processing cracks during machining of parts.
  • the temperature exceeds 850 ° C. plate-like defects are caused by high temperature annealing, and baking hardening characteristics are hardly shown. Therefore, in the present invention, the continuous annealing temperature range is preferably limited to 760 ° C to 850 ° C, and more preferably to 770 ° C to 810 ° C.
  • the continuous annealing steel sheet is first cooled to an average cooling rate of 3 ° C./s or more to a temperature range of 630 to 670 ° C.
  • the primary cooling temperature section 630 ⁇ 670 °C is a temperature section in which ferrite or pearlite (hereinafter referred to as "P" phase) is usually formed.
  • P ferrite or pearlite
  • the higher the cooling rate is advantageous, but the upper limit is not limited because the cooling rate can not be unconditionally faster due to the manufacturing characteristics of the field, but when the cooling rate is less than 3 °C / s, the yield ratio is higher because the yield phase can be formed Does not meet
  • the primary cooling rate is important, if the temperature is less than 630 °C too low carbon (C) diffusion activity is not sufficiently diffused to the austenite system, the concentration of carbon (C) in the ferrite is disadvantageous to ensure ductility. It is also advantageous in terms of the above mentioned properties to exceed 670 ° C., but the problem may arise that too quenching is necessary in subsequent cooling processes.
  • the cold-rolled cold rolled steel sheet is immersed in a zinc plating bath to perform zinc plating, and then cooled to an average secondary cooling rate of 4 ° C./s or more to a temperature of Ms-200 ° C. or lower, thereby. It is possible to produce a hot-dip galvanized steel sheet excellent in aging resistance and baking hardening. Meanwhile, Ms may be defined by the following [Relationship 5].
  • the martensite phase if the martensite phase is formed before the passage of the typical hot dip galvanizing bath temperature range of 440 to 480 ° C., the martensite phase tends to coarsen at the end, and thus the resistance ratio cannot be obtained. Therefore, in this invention, it is preferable to carry out on the conditions of Ms-200 degreeC or less, since the intensity
  • the cooling rate is also preferably performed at 4 ° C / s or more as possible on-site manufacturing conditions.
  • the faster the secondary cooling rate the more advantageous, but in view of the field production conditions, it is preferable to increase the strength of the martensite phase formed by maintaining the cooling rate of at least 4 °C / s as much as possible.
  • the hot dip galvanizing treatment may be performed by immersing in a plating bath (Pot) in the temperature range of the typical temperature range of 440 ⁇ 480 °C.
  • Pot plating bath
  • the present invention is not limited to these specific hot dip galvanizing conditions.
  • alloying after performing hot dip galvanizing, alloying may be performed for 20 seconds or more at a temperature range of 460 to 610 ° C. to produce an alloyed hot dip galvanized steel sheet. Subsequently, the alloyed hot-dip galvanized steel sheet may be manufactured by cooling at an average cooling rate of 4 ° C./s or more to a temperature of Ms-200 ° C. or less.
  • the alloying temperature range in this invention is not specifically limited, The temperature range which the normal alloying process is easy is set. However, when the alloying treatment temperature is less than 460 °C, it is impossible to realistically alloy, and if it exceeds 610 °C alloying degree is too high may cause surface defects during processing.
  • the holding time is preferably 20 seconds or more for the minimum alloying degree, and the upper limit thereof is not particularly limited in view of alloying degree and productivity. Other conditions are the same as in the case of the hot-dip galvanized steel sheet described above.
  • Table 1 After preparing the steel slab of the steel composition shown in Table 1, using a manufacturing process as shown in Table 2 to prepare a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet.
  • the invention steels 1,2,4,6,8 were used for the manufacture of hot dip galvanized (GI) steel sheets, and 3,5 were used for producing the alloyed hot dip galvanized steel (GA).
  • GI hot dip galvanized
  • GA alloyed hot dip galvanized steel
  • 11 and 12 steels were used for the GA steel sheet, and the rest were used to manufacture the GI steel sheet.
  • the tensile test for each test piece was carried out in the C direction using the JIS standard, the fraction of the martensite phase of the second phase including the ferrite phase as the main phase in the microstructure is known structure at a point of 1 / 4t of the plate thickness of the steel sheet.
  • Martensite first calculated the area ratio through Lepelar corrosion using an optical microscope, and observed it again using SEM (3000 times), and then accurately measured and corrected through Count Point operation.
  • the average Mn concentration wt% (a) on the martensite phase and the average Mn concentration wt% (b) on the ferrite within 1 ⁇ m around the martensite phase at the 1 / 4t point of the steel sheet were fabricated using a TEM.
  • Mn concentration ratio (wt%) of each phase was measured by 10 Points or more, and the average was represented as a representative value.
  • the yield strength before temper rolling is 210MPa or less and the yield ratio is 0.55 or less.
  • the BH property was more than 45MPa, and YP-El did not appear at all in the tensile test after artificial aging at 100 ° C ⁇ 1hr.
  • the microstructure of the steel sheet is composed of 95% or more of ferrite and the balance of the second phase, and the percentage of martensite present in the ferrite grain boundary in area% is 90% or more.
  • the difference between the average Mn concentration wt% (a) on the martensite phase and the average Mn concentration wt% (b) on the ferrite phase within 1 ⁇ m around the martensite phase at a point / 4t is basically 0.3 wt% or more. It can be seen that the target material properties can be secured.
  • Mn concentration ratio (wt%) of each phase was measured by 10 points or more by using the Point method using a TEM, and the average is represented as a representative value.
  • the difference between the average Mn concentration wt% (a) in the martensite phase and the average Mn concentration wt% (b) in the ferrite phase within 1 ⁇ m around the martensite phase is 0.3 wt.
  • the higher the hardness of the martensite phase is in accordance with the present invention.
  • the Mn content contained in the martensite phase must be higher than that of the surrounding ferrite phase.
  • the higher the difference in Mn concentration (wt%) between the martensite phase and the ferrite phase within 1 ⁇ m around the martensite phase is advantageous. When the difference in Mn concentration is less than 0.3 wt%, carbon (C) does not easily diffuse into the ferrite phase during baking, and thus the inferior curing property is inferior.
  • Figure 2 is a graph showing a TEM tissue picture formed with a martensite phase around the ferrite phase at the 1 / 4t point of the steel sheet according to an embodiment of the present invention, many potentials are formed around the martensite phase
  • the close relationship with Employment C in the organization suggests that BH is occurring.
  • Comparative Example 1-6 has a high ratio of the fine martensite area of less than 1 ⁇ m average diameter or the area ratio of the ferrite phase is basically low. Therefore, the excellent BH properties desired in the present invention are not secured or some aging problems have occurred.
  • Comparative Example 7-11 in which the steel composition itself is out of the scope of the present invention, basically has a high ratio of fine martensite having an average diameter of 1 ⁇ m or less, and the characteristics of the component itself are not satisfied, thereby securing the properties required by the present invention. I could not.
  • Comparative Example 9-11 did not satisfy the Mneq of [Relationship 1], it could not secure the physical properties required in the present invention.
  • Comparative Example 7-8 the conditions of [Relationship 1] and Mn (wt%) / (1.15 ⁇ Cr (wt%)) are satisfied, but the C content in the steel is outside the scope of the present invention, which is also required by the present invention. could not secure physical properties.

Abstract

Provided are a hot-dip galvanized steel sheet and a hot-dip galvannealed steel sheet with excellent shelf life and bake hardenability, and a method for manufacturing the same. The present invention relates to a hot-dip galvanized steel sheet with excellent shelf life and bake hardenability, the hot-dip galvanized steel sheet having a molten zinc plated layer on the surface of a base steel sheet, wherein the base steel sheet comprises: 0.002-0.012 wt% of carbon (C); 1.6-2.7 wt% of manganese (MN); 0.03 wt% or less (excluding 0 wt%) of phosphorus (P); 0.01 wt% or less (excluding 0 wt%) of sulfur (S); 0.01 wt% or less (excluding 0 wt%) of nitrogen (N); 0.02-0.06 wt% of aluminum (sol.Al); 1.0 wt% or less (excluding 0 wt%) of chromium (Cr), with the remainder being iron and inevitable impurities; the base steel sheet satisfies the relation of 1.3≤Mn(wt%)/(1.15×Cr(wt%))≤20.5; Mneq defined by relational expression 1 satisfies 1.9≤Mneq≤3.9; the microstructure of the steel comprises an area ratio of 95% or more of ferrite, with the remainder being a hard second phase; an occupation ratio of martensite existing in a ferrite grain boundary defined by relational expression 2 is 90% or more; and the difference between the average Mn concentration wt% (a) in a martensite phase at a 1/4t point of the base steel sheet and the average Mn concentration wt% (b) in a ferrite phase within 1 ㎛ from the martensite phase, defined by relational expression 3, is 0.3 wt% or more.

Description

내시효성 및 소부경화성이 우수한 용융아연도금강판, 합금화 용융아연도금강판 및 그 제조방법Hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet with excellent aging resistance and hardening hardening and its manufacturing method
본 발명은 자동차 외판용 소재에 관한 것으로, 보다 상세하게는, 내시효성과 소부경화성이 우수하여 원거리 운송시에도 시효에 의한 표면결함 발생이 없어 자동차용 외판 판넬용 등으로 적용할 수 있는 냉연강판, 용융아연도금강판, 합금화 용융아연도금강판 및 이들의 제조방법에 관한 것이다.The present invention relates to a material for automotive exterior, more specifically, cold-rolled steel sheet that can be applied to the exterior panel panels for automobiles because there is no surface defects caused by aging even during long distance transportation because of excellent aging resistance and hardening hardening, It relates to a hot-dip galvanized steel sheet, an alloyed hot-dip galvanized steel sheet and a manufacturing method thereof.
자동차 외판용 소재는 외부로부터 충격에 안전하게 표면이 보호되도록 하기 위하여 항복강도가 높은 강판이 요구된다. 이는 내덴트성을 향상시켜 주행중 외판에 결함이 발생치 않도록 하기 위해 가능한 한 항복강도가 높은 강판을 사용하여 내덴트성 및 경량화에 기여하고 있다. In order to protect the surface of the vehicle from external impacts, the steel sheet has a high yield strength. This contributes to the dent resistance and light weight by using a steel sheet with high yield strength as much as possible in order to improve the dent resistance to prevent defects in the outer shell during driving.
종래, 도어, 트렁크리드 및 펜더와 같은 우수한 내덴트성이 요구되는 자동차 외판 패널에는 인장강도 340MPa 클래스의 BH 강판(소부경화형 강판)이 주로 적용되어 왔고, 최근 내덴트성 평가로 항복강도의 중요도가 높아짐에 따라 항복강도 기준으로는 180MPa 이상을 갖도록 설계되어 외판재에 적용하고 있다. 이에 항복강도 증가에 따른 두께감소로 경량화에 보다 기여하고자 항복강도 기준 210MPa, 240MPa, 260MPa급의 고강도 소부경화형 강판이 개발되어 양산 적용을 추진하고 있는 중이다.Conventionally, BH steel sheet (baking hardened steel sheet) of tensile strength 340 MPa class has been mainly applied to automobile exterior panel panels requiring excellent dent resistance such as doors, trunk lids and fenders, and the importance of yield strength is recently evaluated by dent resistance evaluation. As it increases, it is designed to have more than 180MPa as the yield strength criterion and is applied to outer board. Therefore, in order to contribute more to the weight reduction due to the increase in yield strength, high-strength hardening hardened steel sheets of 210 MPa, 240 MPa, and 260 MPa grades have been developed and are being mass-produced.
그러나 이러한 강 종들은 대부분 극저탄소강을 베이스로 미량의 Ti 혹은 Nb함량을 효과적으로 제어하여 소부경화성을 확보하고 있으나, 제강 조업시 C의 함량 범위의 편차로 인해 소부경화성(이하, "BH"성이라 한다)이 달라질 뿐만 아니라 일부 BH성이 높아지면 역으로 내시효특성(이하, "AI"특성이라 한다)이 열위되어 장거리 운송에 따른 시효발생으로 부품 가공시 표면 결함이 발생 되어 문제가 되어왔다. However, most of these steels are based on ultra-low carbon steel to effectively control the small amount of Ti or Nb content to secure the hardening hardening, but due to the variation of the C content range during steelmaking operation, the hardening hardening (hereinafter referred to as "BH") In addition, when some BH properties are increased, the aging characteristics (hereinafter, referred to as "AI" characteristics) are inferior, and surface defects occur during machining of parts due to aging caused by long distance transportation.
즉, BH성이 증가하면 내시효성이 열화된다. 내시효성의 열화는 장거리 운송 및 부품 가공 전 창고에서 장시간 보관에 따른 시효 발생으로서, 프레스 후의 외판 표면에 주름 현상이 나타나는 표면결함을 야기시켜 소부경화형 강판으로서 많은 문제점을 안고 있다. 따라서 BH성이 우수하면서도 내시효특성 또한 우수하여 시효문제가 거의 발생하지 않은 복합조직(페라이트 + 마르텐사이트)형 BH강판을 제조할 수 있는 기술개발에 대한 요구가 대두하고 있다.In other words, as BH resistance increases, aging resistance deteriorates. Deterioration of aging resistance is the generation of aging due to long-term storage in the warehouse before long-distance transportation and parts processing, causing a surface defect that appears wrinkles on the surface of the outer plate after pressing has a number of problems as a hardening hardened steel sheet. Therefore, there is a demand for technology development that can produce a composite structure (ferrite + martensite) type BH steel sheet having excellent BH resistance and excellent aging resistance and hardly causing aging problems.
이러한 복합조직형 소부경화형 강판은 조직 내 형성된 마르텐사이트(M)상 주변에 가동 전위로 인해 우수한 소부경화 특성이 나타난 반면, 내시효특성이 우수하다. 하지만 이러한 복합조직형 강판을 제조하기 위해서는 기본적으로 적정 수준 이상의 C, Mn, Cr등 경화능 원소 첨가가 필수적이어서 오히려 항복강도가 낮은 복합조직강을 제조하기가 어렵다.The composite hardening hardening type steel sheet exhibits excellent hardening hardening characteristics due to a movable potential around the martensite (M) phase formed in the tissue, but has excellent aging resistance. However, in order to manufacture such a composite steel sheet, it is essential to add a hardenable element such as C, Mn, Cr or higher than an appropriate level, so it is difficult to produce a composite steel with low yield strength.
한편, 자동차용으로 적합하게 적용되기 위해서는 우수한 내식성이 요구되며, 이에 종래부터 자동차용 강판으로서 내식성이 우수한 용융아연도금강판이 사용되어 왔다. 이러한 강판은 재결정 소둔 및 도금을 동일 라인에서 실시하는 연속 용융아연 도금설비를 통해 제조되므로 저비용으로 고내식성의 강판을 제조할 수 있는 장점이 있다. 또한, 용융아연도금 후에 다시 가열처리한 합금화 용융아연도금강판은 우수한 내식성과 더불어 용접성이나 성형성도 우수하여 널리 사용되고 있다.On the other hand, in order to be suitably applied for automobiles require excellent corrosion resistance, there has been conventionally used a hot-dip galvanized steel sheet excellent in corrosion resistance as a steel sheet for automobiles. Since the steel sheet is manufactured through a continuous hot dip galvanizing apparatus which performs recrystallization annealing and plating in the same line, there is an advantage that a steel sheet having high corrosion resistance can be manufactured at low cost. In addition, the alloyed hot-dip galvanized steel sheet which has been heat-treated again after hot-dip galvanizing is widely used because of its excellent corrosion resistance and excellent weldability and formability.
이러한 복합조직형 소부경화형 강판으로 특허문헌 1(일본 공개특허공보 제 2010-0023025호)에는 C함량을 0.01~0.12%, Mn함량을 2%미만으로 하고, 제2상 평균 입장경의 면적율을 관리하고 소둔시 가열속도를 3℃/sec이하로 관리함으로써 BH성이 우수한 소부경화강을 제조하고 있으나, 소둔 시 너무 느린 가열속도로 인하여 실제 양산 제조시 경제성 효과가 미흡할 뿐만 아니라 특히, C함량이 0.02% 수준으로 항복강도가 230MPa급 이상으로 높아 이 역시 부품 가공시 표면결함 발생이 높은 문제점이 있다.In this composite structure-type hardened steel sheet, Patent Document 1 (Japanese Patent Laid-Open No. 2010-0023025) has a C content of 0.01 to 0.12% and an Mn content of less than 2%, and manages the area ratio of the second phase average entrance diameter. The annealing hardening steel with excellent BH is manufactured by managing the heating rate at annealing rate of 3 ℃ / sec or less, but due to the too slow heating rate during annealing, not only economic effect is insufficient in actual mass production but especially, C content is 0.02 Yield strength is higher than 230MPa level at the level of%, which also causes high surface defects when machining parts.
특허문헌 2(일본 공개특허공보 제 2012-0025591호)에는 C함량이 0.015%를 초과하는 강판을 대상으로 P함량을 0.015~0.05%로 제어하여 복합조직형 소부경화강을 제조하고 있으나, 인장강도가 440MPa급 이상이며 항복강도 역시 220MPa 부근으로서 기존 340BH강의 항복강도 180MPa급을 대체하기가 곤란하며, 일부 베이나이트(B)상을 포함하여 구멍확장능을 향상시켰으나 이 역시 부품 성형시 높은 항복강도로 인해 표면결함 발생 가능성이 높은 문제점이 있다.Patent Document 2 (Japanese Laid-Open Patent Publication No. 2012-0025591) manufactures a composite structure-type hardened hardened steel by controlling the P content to 0.015 to 0.05% for steel sheets having a C content of more than 0.015%. Is over 440MPa class and the yield strength is around 220MPa.It is difficult to replace the yield strength of the existing 340BH steel with 180MPa class.In addition, some bainite (B) phases have improved hole expandability, but this also provides high yield strength when forming parts. Due to this, there is a high possibility of surface defects.
특허문헌 3(일본 공개특허공보 제 2009-035818호)에서도 강 중 조직 내 일부 베이나이트가 포함되어 인장 강도 대비 항복강도가 상승하여 표면 결함 문제를 야기할 수 있으며, Cr함량이 0.5%를 초과함으로써 강판 표면에 Cr계 산화물이 형성되어 열간압연 시 스케일 제거가 곤란하여 외판재로서 표면 결함을 다수 함유할 수 있으므로 표면이 미려한 외판 강재를 제조하는데 단점을 지니고 있다.Patent Document 3 (Japanese Patent Laid-Open Publication No. 2009-035818) also includes some bainite in the steel structure in steel, which leads to an increase in yield strength relative to tensile strength, which may cause surface defect problems, and the Cr content exceeds 0.5%. Since Cr-based oxide is formed on the surface of the steel sheet, it is difficult to remove the scale during hot rolling, and thus it may contain a large number of surface defects as the outer sheet material, which has disadvantages in manufacturing the outer sheet steel having a beautiful surface.
따라서 본 발명은 상술한 종래기술의 한계를 극복하기 위한 것으로, 강 조성성분 및 제조공정을 최적화하여 소부경화성과 내시효특성이 우수한 항복강도 170MPa 이상의 자동차 외판용 강판으로 적합한 용융아연도금강판 내지 합금화 용융아연도금강판을 제공함을 그 목적으로 한다.Accordingly, the present invention is to overcome the limitations of the prior art described above, by optimizing the steel composition and the manufacturing process, the hot-dip galvanized steel sheet or alloyed melting suitable for steel sheet for automotive exterior plate having a yield strength of 170MPa or more excellent in hardening hardening resistance and aging characteristics The purpose is to provide galvanized steel sheets.
또한 본 발명은 상기 용융아연도금강판 내지 합금화 용융아연도금강판을 제조하는 방법을 제공함을 그 목적으로 한다. In addition, an object of the present invention is to provide a method for producing the hot-dip galvanized steel sheet to the alloyed hot-dip galvanized steel sheet.
그러나 본 발명이 해결하고자 하는 과제는 이상에서 언급한 과제로 제한되지 않으며, 언급되지 않은 또 다른 과제들은 아래의 기재로부터 당업자에게 명확하게 이해될 수 있을 것이다.However, the problem to be solved by the present invention is not limited to the above-mentioned problem, another task that is not mentioned will be clearly understood by those skilled in the art from the following description.
상기 목적을 달성하기 위한 본 발명은,The present invention for achieving the above object,
소지강판 표면에 용융아연도금층이 형성되어 있는 용융아연도금강판으로서,A hot-dip galvanized steel sheet having a hot-dip galvanized layer formed on the surface of the base steel sheet,
상기 소지강판은 중량%로, 탄소(C):0.002~0.012%, 망간(Mn):1.6~2.7%, 인(P):0.03% 이하(0%는 제외), 황(S): 0.01% 이하(0%는 제외), 질소(N):0.01% 이하(0%는 제외), 알루미늄(sol.Al): 0.02~0.06%, 크롬(Cr):1.0% 이하(0%는 제외), 잔부 철 및 불가피한 불순물을 포함하여 조성되고, 또한 1.3≤Mn(wt%)/(1.15×Cr(wt%))≤20.5의 관계를 만족하고, 하기 관계식 1에 의해 정의되는 Mneq가 1.9≤Mneq≤3.9를 만족하며, The steel sheet is in weight%, carbon (C): 0.002 ~ 0.012%, manganese (Mn): 1.6 ~ 2.7%, phosphorus (P): 0.03% or less (excluding 0%), sulfur (S): 0.01% Or less (excluding 0%), nitrogen (N): 0.01% or less (excluding 0%), aluminum (sol.Al): 0.02 to 0.06%, chromium (Cr): 1.0% or less (excluding 0%), It is composed of the balance of iron and unavoidable impurities, and satisfies the relationship of 1.3 ≦ Mn (wt%) / (1.15 × Cr (wt%)) ≦ 20.5, and Mneq defined by the following equation 1 is 1.9 ≦ Mneq ≦ Satisfies 3.9,
그 강 미세조직이 면적비로 95% 이상의 페라이트와 잔부 경질 제 2상으로 이루어지며,The steel microstructure consists of 95% or more of ferrite and the remaining hard second phase by area ratio,
하기 관계식 2에 의해 정의되는 페라이트 결정립계에 존재하는 마르텐사이트 점유비율이 90% 이상이며, 그리고 Martensite occupancy in the ferrite grain boundary defined by the following relation 2 is 90% or more, and
하기 관계식 3에 의해 정의되는, 소지강판 1/4t지점에서 마르텐사이트 상에서의 평균 Mn 농도 wt%(a)와 상기 마르텐사이트 상 주변 1㎛이내의 페라이트 상에서의 평균 Mn 농도 wt%(b)의 차가 0.3wt%이상인 것을 특징으로 하는 내시효성 및 소부경화성이 우수한 용융아연도금강판에 관한 것이다.The difference between the average Mn concentration wt% (a) on martensite and the average Mn concentration wt% (b) on ferrite within 1 µm around the martensite phase, defined by the following equation (3) It relates to a hot-dip galvanized steel sheet excellent in aging resistance and baking hardening, characterized in that more than 0.3wt%.
[관계식 1][Relationship 1]
Mneq = Mn + 0.45Si + 2P + 1.15CrMneq = Mn + 0.45Si + 2P + 1.15Cr
[관계식 2][Relationship 2]
P(%) = {Pgb/(Pg+Pgb)}×100 P (%) = {Pgb / (Pg + Pgb)} × 100
(여기서, P: 페라이트 결정립계에 존재하는 마르텐사이트 점유율, Pgb: 페라이트 결정립계에 존재하는 마르텐사이트 점유 면적, Pg: 페라이트 결정립내에 존재하는 마르텐사이트 점유 면적을 나타낸다)(Here, P: shows martensite occupancy in the ferrite grain boundary, Pgb: martensite occupancy area in the ferrite grain boundary, Pg: shows the martensite occupancy area in the ferrite grain)
[관계식 3][Relationship 3]
a-b ≥ 0.3wt%a-b ≥ 0.3wt%
(여기서, a는 소지강판 1/4t지점에서 마르텐사이트 상에서의 평균 Mn 농도(wt%), 그리고 b는 상기 마르텐사이트 상 주변 1㎛이내의 페라이트 상에서의 평균 Mn 농도(wt%)를 나타낸다.)(Where a denotes the average Mn concentration (wt%) on martensite at 1 / 4t of the base steel sheet, and b denotes the average Mn concentration (wt%) on ferrite within 1 μm around the martensite phase.)
상기 소지강판은 보론(B):0.003% 이하(0%는 제외) 및 몰리브덴(Mo): 0.2% 이하(0%는 제외) 중에 1종 이상을 추가로 포함할 수 있다. The steel sheet may further include one or more of boron (B): 0.003% or less (excluding 0%) and molybdenum (Mo): 0.2% or less (excluding 0%).
상기 제 2상을 이루는 마르텐사이트 상 중에서 평균직경 1㎛이하의 미세 마르텐사이트 면적%가 2%이하(0%제외)인 것이 바람직하다.It is preferable that the area of fine martensite having an average diameter of 1 µm or less is 2% or less (excluding 0%) of the martensite phase forming the second phase.
상기 소지강판은 조질압연 전 항복강도가 210MPa급 이하이며 항복비가 0.55이하일 수가 있다. The steel sheet may have a yield strength of less than 210MPa and a yield ratio of less than 0.55 before temper rolling.
상기 용융아연도금강판의 용융아연도금층을 합금화처리함으로써 내시효성 및 소부경화성이 우수한 합금화 용융아연도금강판에 관한 것이다. The present invention relates to an alloyed hot dip galvanized steel sheet having excellent aging resistance and baking hardening property by alloying the hot dip galvanized layer of the hot dip galvanized steel sheet.
또한 본 발명은, 중량%로, 탄소(C):0.002~0.012%, 망간(Mn):1.6~2.7%, 인(P):0.03% 이하(0%는 제외), 황(S): 0.01% 이하(0%는 제외), 질소(N):0.01% 이하(0%는 제외), 알루미늄(sol.Al): 0.02~0.06%, 크롬(Cr):1.0% 이하(0%는 제외), 잔부 철 및 불가피한 불순물을 포함하고, 또한 1.3≤Mn(wt%)/(1.15×Cr(wt%))≤20.5의 관계를 만족하고, 상기 관계식 1에 의해 정의되는 Mneq가 1.9≤Mneq≤3.9를 만족하는 강 슬라브를 마련한 후, 이를 재가열하는 공정;In the present invention, by weight%, carbon (C): 0.002-0.012%, manganese (Mn): 1.6-2.7%, phosphorus (P): 0.03% or less (excluding 0%), sulfur (S): 0.01 % Or less (excluding 0%), nitrogen (N): 0.01% or less (excluding 0%), aluminum (sol.Al): 0.02 to 0.06%, chromium (Cr): 1.0% or less (excluding 0%) , Balance iron and unavoidable impurities, satisfying the relationship of 1.3 ≦ Mn (wt%) / (1.15 × Cr (wt%)) ≦ 20.5, and Mneq defined by the above equation 1 is 1.9 ≦ Mneq ≦ 3.9 After preparing a steel slab satisfying the step, reheating it;
상기 재가열된 강 슬라브를 Ar3+20℃~950℃의 온도범위에서 마무리 열간압연한 후, 450~700℃에서 권취하는 공정;A step of winding the reheated steel slab at a temperature range of Ar 3 + 20 ° C. to 950 ° C., followed by winding at 450 to 700 ° C .;
상기 권취된 열연강판을 40~80%의 압하율로 냉간압연하고, 후속하여, 760℃~850℃의 온도범위로 연속 소둔하는 공정; Cold rolling the wound hot rolled steel sheet at a reduction ratio of 40 to 80%, and subsequently performing continuous annealing at a temperature range of 760 ° C to 850 ° C;
상기 연속소둔된 강판을 630~670℃의 온도범위까지 평균냉각속도 3℃/s 이상으로 1차 냉각한 후, 아연 도금욕에 침지하여 용융아연도금을 행하고, 이어 Ms-200℃ 이하의 온도까지 4℃/s 이상의 평균 냉각속도로 2차 냉각하는 공정;을 포함하는 내시효특성 및 소부경화성이 우수한 용융아연도금강판의 제조방법에 관한 것이다.The continuous annealed steel sheet was first cooled to an average cooling rate of 3 ° C./s or more to a temperature range of 630 ° C. to 670 ° C., and then immersed in a zinc plating bath to perform hot dip galvanizing, followed by a temperature of Ms-200 ° C. or lower. It relates to a method for producing a hot-dip galvanized steel sheet excellent in aging resistance and baking hardening resistance, including; step of secondary cooling at an average cooling rate of 4 ℃ / s or more.
상기 강 슬라브는 보론(B):0.003% 이하(0%는 제외) 및 몰리브덴(Mo): 0.2% 이하(0%는 제외) 중에 1종 이상을 추가로 포함할 수 있다. The steel slab may further include at least one of boron (B): 0.003% or less (excluding 0%) and molybdenum (Mo): 0.2% or less (excluding 0%).
또한 상기 2차 냉각으로 제조되는 용융아연도금강판을 이루는 소지강판은, In addition, the base steel sheet to form a hot-dip galvanized steel sheet produced by the secondary cooling,
그 강 미세조직이 면적비로 95% 이상의 페라이트와 잔부 경질 제 2상으로 이루어지며,The steel microstructure consists of 95% or more of ferrite and the remaining hard second phase by area ratio,
상기 관계식 2에 의해 정의되는 페라이트 결정립계에 존재하는 마르텐사이트 점유비율이 90% 이상이며, 그리고 Martensite occupancy in the ferrite grain boundary defined by the above relationship 2 is 90% or more, and
상기 관계식 3에 의해 정의되는, 소지강판 1/4t지점에서 마르텐사이트 상에서의 평균 Mn 농도 wt%(a)와 상기 마르텐사이트 상 주변 1㎛이내의 페라이트 상에서의 평균 Mn 농도 wt%(b)의 차가 0.3wt%이상일 수가 있다.The difference between the average Mn concentration wt% (a) on martensite and the average Mn concentration wt% (b) on ferrite within 1 µm around the martensite phase, as defined by Equation 3 above, It may be 0.3 wt% or more.
또한 상기 제 2상을 이루는 마르텐사이트 상 중에서 평균직경 1㎛이하의 미세 마르텐사이트 면적%가 2%이하(0%제외)인 것이 바람직하다. In addition, it is preferable that the area of fine martensite having an average diameter of 1 m or less in the martensite phase forming the second phase is 2% or less (excluding 0%).
또한 본 발명은, 상기 1차 냉각 후, 아연 도금욕에 침지하여 용융아연도금을 행하고, 이어 460~610℃의 온도역에서 합금화처리를 행한 후 Ms-200℃ 이하의 온도까지 4℃/s 이상의 평균 냉각속도로 2차 냉각하는 것을 특징으로 하는 내시효특성 및 소부경화성이 우수한 합금화 용융아연도금강판의 제조방법에 관한 것이다. In addition, the present invention, after the primary cooling, immersed in a zinc plating bath to perform hot dip galvanizing, followed by an alloying treatment in the temperature range of 460 ~ 610 ℃, 4 ℃ / s or more to a temperature of Ms-200 ℃ or less The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet excellent in aging resistance and baking hardening, characterized by secondary cooling at an average cooling rate.
상술한 구성의 본 발명은, 내시효성과 소부경화성을 동시에 우수하게 확보할 수 있는 용융아연도금강판 내지 합금화 용융아연도금강판을 제공할 수 있으며, 이는 장거리 운송시 시효결함 발생이 없는 자동차 외판용으로 적합한 효과가 있다.The present invention having the above-described configuration can provide a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet which can ensure excellent aging resistance and baking hardening at the same time, which is used for automobile exterior plates without the occurrence of aging defects during long distance transportation. There is a suitable effect.
도 1 본 발명의 일실시예에 따른 소지강판 1/4t지점에서 마르텐사이트(M)상에서의 평균 Mn 농도 wt%(a)와 상기 마르텐사이트(M)상 주변 1㎛이내 페라이트 상에서의 평균 Mn 농도 wt%(b)차이를 보여주는 그래프이다. 1 is a mean Mn concentration of wt% (a) on martensite (M) and the average Mn concentration on the ferrite within 1㎛ around the martensite (M) at the 1 / 4t point of the steel sheet according to an embodiment of the present invention It is a graph showing the difference of wt% (b).
도 2는 본 발명의 일실시예에 따른 소지강판의 1/4t 지점에서의 페라이트(F)상 주변에 마르텐사이트(M)상이 형성되어 있는 TEM 조직사진을 보여주는 그래프이다. FIG. 2 is a graph showing a TEM tissue photograph in which a martensite (M) phase is formed around a ferrite (F) phase at a 1 / 4t point of the base steel sheet according to an embodiment of the present invention.
본 발명자들은 자동차 외판용으로 적합하도록 내시효성과 소부경화성을 동시에 확보하여 성형성이 우수한 강판을 제공하기 위하여 깊이 연구한 결과, 합금설계와 더불어 제조조건을 최적화시킴으로써 의도하는 물성을 만족하는 복합조직강판을 제공할 수 있음을 확인하고, 본 발명을 완성하기에 이르렀다.The present inventors have studied in depth to provide a steel sheet with excellent moldability by securing both aging resistance and hardening hardenability to be suitable for automotive exterior panels, composite steel sheet that satisfies the intended properties by optimizing the manufacturing conditions with alloy design It was confirmed that it can provide, and came to complete the present invention.
이하, 본 발명에 대하여 상세히 설명한다.EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.
먼저, 본 발명의 내시효성과 소부경화성이 우수한 용융아연도금강판 내지 합금화 용융아연도금강판에 대하여 상세히 설명한다.First, the hot-dip galvanized steel sheet or the alloyed hot-dip galvanized steel sheet excellent in the aging resistance and baking hardening property of the present invention will be described in detail.
본 발명의 냉연강판(소지강판), 또는 용융아연도금강판 내지 합금화 용융아연도금강판을 이루는 소지강판은, 중량%로, 탄소(C):0.002~0.012%, 망간(Mn):1.6~2.7%, 인(P):0.03% 이하(0%는 제외), 황(S): 0.01% 이하(0%는 제외), 질소(N):0.01% 이하(0%는 제외), 알루미늄(sol.Al): 0.02~0.06%, 크롬(Cr):1.0% 이하(0%는 제외), 잔부 철 및 불가피한 불순물을 포함하여 조성되며, 이하, 그 합금성분 및 제한하는 이유에 대하여 상세히 설명한다. 이때, 특별한 언급이 없는 한 각 성분의 함량은 모두 중량%를 의미한다.The cold-rolled steel sheet of the present invention, or the steel sheet comprising the hot-dip galvanized steel to the alloyed hot-dip galvanized steel, in weight%, carbon (C): 0.002-0.012%, manganese (Mn): 1.6-2.7% , Phosphorus (P): 0.03% or less (excluding 0%), sulfur (S): 0.01% or less (excluding 0%), nitrogen (N): 0.01% or less (excluding 0%), aluminum (sol. Al): 0.02 to 0.06%, chromium (Cr): 1.0% or less (except 0%), including residual iron and unavoidable impurities. Hereinafter, the alloy component and the reason for limitation will be described in detail. At this time, unless otherwise specified, the content of each component means all by weight.
C: 0.002~0.012%C: 0.002-0.012%
탄소(C)는 본 발명에서 제 2상을 확보하여 복합조직을 갖는 강판을 제조하는데 중요한 성분으로서, 이는 2상 조직 중의 하나인 마르텐사이트를 형성시켜 강도를 확보하는데에 유리한 원소이다. 일반적으로 C의 함량이 증가할수록 마르텐사이트의 형성이 용이하여 복합조직강 제조에 유리하나, 최적의 복합조직강을 만드는데는 그 함량제어가 중요하다. C 함량이 지나치게 적으면, 충분한 제 2상의 면적율을 확보할 수 없어 복합조직강에 의해 내시효성이 우수한 소부경화형 강판의 제조가 불가능하다. 한편 C 함량이 지나치게 높으면 복합조직강의 형성에는 유리하지만 항복강도가 상승하여 고객 부품가공시 표면에 굴곡 결함의 발생 경향이 높아질 뿐만 아니라 조질압연 전 항복강도 210MPa이하의 복합조직강을 얻을 수 없다. Carbon (C) is an important component in securing a second phase in the present invention to produce a steel sheet having a composite structure, which is an element that is advantageous for securing strength by forming martensite, which is one of the two phase structures. In general, as the content of C increases, martensite is more easily formed, which is advantageous for the production of composite tissue steel. However, the content control is important for making an optimal composite steel. If the C content is too small, a sufficient area ratio of the second phase cannot be secured, and therefore, the composite hardened steel cannot be used to manufacture a bake hardened steel sheet having excellent aging resistance. On the other hand, if the C content is too high, it is advantageous for the formation of composite tissue steel, but the yield strength is increased to increase the occurrence of bending defects on the surface of the customer's parts, and it is not possible to obtain the composite tissue steel of 210 MPa or less before temper rolling.
본 발명에서는 가능한 한 C 함량을 최적화하여, 낮은 C 함량에서도 내시효성이 우수한 소부경화형 복합조직강을 제조하는데 목적이 있다. 만일 C 함량이 0.002% 미만이면 복합조직강을 얻을 수 없으며, C 함량이 0.012%를 초과하면 복합조직강을 얻을 수 있으나 항복강도가 상승하여 일반적으로 표면특성이 우수한 소부경화강을 공급할 수가 없다. 따라서 본 발명에서는 C 함량을 0.002~0.012% 범위로 제한함이 바람직하며, 보다 바람직하게는 0.004~0.01% 범위로 제한하는 것이다. In the present invention, by optimizing the C content as much as possible, it is an object to produce a hardening hardened composite steel having excellent aging resistance even at low C content. If the C content is less than 0.002%, the composite tissue steel cannot be obtained. If the C content is more than 0.012%, the composite tissue steel can be obtained, but the yield strength is increased, so that it is generally impossible to supply the hardened hardened steel having excellent surface properties. Therefore, in the present invention, it is preferable to limit the C content to 0.002 to 0.012% range, more preferably to 0.004 to 0.01% range.
Mn: 1.6~2.7%Mn: 1.6-2.7%
망간(Mn)은 복합조직을 갖는 강판에서 경화능을 향상시키는 원소로서, 특히 마르텐사이트를 형성함에 있어서 중요한 원소이다. 기존 고용강화강에서는 고용강화효과로 강도상승에 유효하고, 강 중 불가피하게 첨가되는 S를 MnS로 석출시켜 열간압연 시 S에 의한 판파단 발생 및 고온취화 현상을 억제시키는 중요한 역할을 한다.Manganese (Mn) is an element that improves hardenability in a steel sheet having a composite structure, and is particularly important in forming martensite. Existing solid solution strengthening steel is effective to increase strength due to the strengthening effect of solid solution, and precipitates S added unavoidably in steel with MnS, which plays an important role in suppressing plate breakage caused by S and high temperature embrittlement during hot rolling.
본 발명에서는 이러한 Mn을 1.6% 이상으로 첨가하는 것이 바람직하며, 만일 그 함량이 1.6% 미만이면 마르텐사이트 형성이 불가하여 복합조직강의 제조가 어려울 뿐만 아니라 인장 시 항복점 연신 특성이 나타나고 항복비가 높아지는 문제점을 나타낸다. 반면 2.7%를 초과하면 마르텐사이트가 과잉으로 형성되어 재질이 불안정하고, 조직 내 Mn-Band(Mn 산화물의 띠)가 형성되어 가공크랙 및 판파단 발생 위험이 높아지는 문제가 있다. 또한 소둔시 Mn 산화물이 표면에 용출되어 도금성을 크게 저해하는 문제가 있다. In the present invention, it is preferable to add more than 1.6% of Mn, and if the content is less than 1.6%, martensite is not formed, and thus, it is difficult to manufacture composite tissue steel. Indicates. On the other hand, if the content exceeds 2.7%, martensite is excessively formed and the material is unstable, and Mn-Band (Mn oxide band) is formed in the tissue, thereby increasing the risk of processing cracks and plate breakage. In addition, there is a problem that Mn oxide is eluted to the surface during annealing to significantly inhibit the plating property.
따라서 본 발명에서는 Mn의 함량을 1.6~2.7%로 제한하는 것이 바람직하며, 보다 바람직하게는 Mn함량을 2.0~2.4%로 제한하는 것이다.Therefore, in the present invention, it is preferable to limit the content of Mn to 1.6 ~ 2.7%, more preferably to limit the Mn content to 2.0 ~ 2.4%.
Cr: 1.0% 이하(0%는 제외)Cr: 1.0% or less (excluding 0%)
크롬(Cr)은 상술한 Mn과 유사한 특성을 갖는 성분으로서, 강의 경화능을 향상시키고 고강도를 확보하기 위해 첨가되는 원소이다. 이러한 Cr은 마르텐사이트 형성에 유효하고, 열간압연 과정에서 Cr23C6과 같은 조대한 Cr계 탄화물을 형성하여 강중 고용 C 량을 적정 수준 이하로 석출시킴으로써 항복점연신(YP-El) 발생을 억제하여 항복비가 낮은 복합조직강 제조에 유리한 원소이다. 또한 강도 상승 대비 연신율 하락을 최소화시켜 고연성을 갖는 복합조직강의 제조에도 유리하다.Chromium (Cr) is a component having properties similar to those of Mn described above, and is an element added to improve the hardenability of steel and to secure high strength. Such Cr is effective in forming martensite, and forms coarse Cr-based carbides such as Cr 23 C 6 in the hot rolling process, thereby suppressing the yield point yield (YP-El) by precipitating the amount of solid solution C in the steel below an appropriate level. It is an advantageous element for the production of composite steel with low yield ratio. In addition, it is advantageous to manufacture composite tissue steel with high ductility by minimizing elongation drop compared to strength increase.
본 발명에서 상기 Cr은 경화능 향상을 통해 마르텐사이트 형성을 용이하게 하지만, 그 함량이 1.0%를 초과하게 되면 마르텐사이트 형성 비율을 과도하게 증가시켜 강도 및 연신율 저하를 초래하는 문제가 있다. 따라서, 본 발명에서는 Cr의 함량을 1.0% 이하로 제한하는 것이 바람직하며, 제조상 불가피하게 첨가되는 양을 고려하여 0%를 제외한다.In the present invention, the Cr facilitates the formation of martensite through improving the hardenability, but if the content exceeds 1.0%, there is a problem of excessively increasing the martensite formation rate, resulting in a decrease in strength and elongation. Therefore, in the present invention, it is preferable to limit the content of Cr to 1.0% or less, and 0% is excluded in consideration of the amount inevitably added in production.
P: 0.03% 이하(0%는 제외)P: 0.03% or less (except 0%)
강 중 인(P)은 성형성을 크게 해지지 않으면서 강도 확보에 가장 유리한 원소이나, 과잉 첨가할 경우 취성 파괴 발생 가능성이 크게 증가하여 열간압연 도중 슬라브의 판파단 발생 가능성이 증가할 뿐만 아니라 도금표면 특성을 저해하는 원소로 작용하는 문제가 있다.Phosphorus (P) in steel is the most favorable element to secure the strength without increasing the formability, but excessive addition greatly increases the possibility of brittle fracture, which increases the possibility of plate breakage of the slab during hot rolling. There is a problem of acting as an element that inhibits properties.
따라서 본 발명에서는 이러한 P의 함량을 최대 0.03%로 제한하며, 다만 불가피하게 첨가되는 수준을 고려하여 0%는 제외한다.Therefore, in the present invention, the content of P is limited to a maximum of 0.03%, but 0% is excluded in consideration of the inevitably added level.
S: 0.01% 이하(0%는 제외)S: 0.01% or less (except 0%)
황(S)은 강 중 불순물 원소로서 불가피하게 첨가되는 원소로서, 가능한 한 낮게 관리하는 것이 중요하다. 특히, 강 중 S은 적열 취성을 발생시킬 가능성을 높이는 문제가 있으므로, 그 함량을 0.01% 이하로 제어하는 것이 바람직하다. 다만 제조과정 중에 불가피하게 첨가되는 수준을 고려하여 0%는 제외한다.Sulfur (S) is an element inevitably added as an impurity element in steel, and it is important to manage it as low as possible. In particular, since S in steel has a problem of increasing the possibility of generating red brittleness, it is preferable to control the content to 0.01% or less. However, 0% is excluded in consideration of the inevitably added level during the manufacturing process.
N: 0.01% 이하(0%는 제외)N: 0.01% or less (except 0%)
질소(N)는 강 중 불순물 원소로서 불가피하게 첨가되는 원소이다. 이러한 N은 가능한 한 낮게 관리하는 것이 중요하나, 이를 위해서는 강의 정련 비용이 급격히 상승하는 문제가 있으므로, 조업조건이 가능한 범위인 0.01% 이하로 제어하는 것이 바람직하다. 다만 불가피하게 첨가되는 수준을 고려하여 0%는 제외한다.Nitrogen (N) is an element inevitably added as an impurity element in steel. It is important to manage such N as low as possible, but for this purpose, there is a problem that the refining cost of the steel rises sharply, it is desirable to control the operating conditions within 0.01% of the possible range. However, 0% is excluded in consideration of the added level.
Sol.Al: 0.02~0.06%Sol.Al: 0.02 ~ 0.06%
산가용 알루미늄(sol.Al)은 강의 입도 미세화와 탈산을 위해 첨가되는 원소로서, 그 함량이 0.02% 미만이면 통상의 안정된 상태로 알루미늄 킬드(Al killed)강을 제조할 수 없다. 한편 그 함량이 0.06%를 초과하면 결정립 미세화 효과로 강도 상승에는 유리한 반면, 제강 연주 조업시 개재물의 과다 형성으로 용융아연도금강판 표면 불량이 발생할 가능성이 높아질 뿐만 아니라 제조원가의 상승을 초래하는 문제가 있다. 따라서 본 발명에서는 sol.Al의 함량을 0.02~0.06%로 제어하는 것이 바람직하다.Acid soluble aluminum (sol.Al) is an element added to refine the particle size and deoxidation of the steel, and if the content is less than 0.02%, aluminum killed steel cannot be manufactured in a normal stable state. On the other hand, if the content exceeds 0.06%, it is advantageous to increase the strength due to the grain refinement effect, while the excessive formation of inclusions during steelmaking operation increases the possibility of surface defects on the hot-dip galvanized steel sheet and also increases the manufacturing cost. . Therefore, in the present invention, it is preferable to control the content of sol.Al to 0.02 to 0.06%.
본 발명에서는 기타 선택원소로서 보론(B)과 몰리브덴(Mo) 중 1종 이상을 포함할 수 있는데, 이들은 경화능을 다소 향상시켜 복합조직강을 제조하는데 도움이 된다In the present invention, other optional elements may include one or more of boron (B) and molybdenum (Mo), which may help to produce a composite tissue steel by slightly improving the hardenability.
B: 0.003% 이하(0%는 제외)B: 0.003% or less (except 0%)
강 중 보론(B)은 P 첨가에 의한 내2차 가공취성을 방지하기 위해 첨가하는 원소이다. 이러한 보론(B)의 함량이 0.003%를 초과하게 되면 연신율의 저하를 초래하는 문제가 있으므로 상기 보론(B)의 함량을 0.003% 이하로 제어하며, 이때 불가피하게 첨가되는 수준을 고려하여 0%는 제외한다.Boron (B) in steel is an element added in order to prevent secondary work brittleness by P addition. When the content of the boron (B) exceeds 0.003%, there is a problem that the elongation is lowered, so the content of the boron (B) is controlled to 0.003% or less, in which case 0% is inevitably added Exclude.
Mo:0.2%이하(0%는 제외)Mo: 0.2% or less (except 0%)
몰리브덴(Mo)은 복합조직을 갖는 강판에서 경화능을 향상시키는 원소로서, 특히 마르텐사이트를 형성함에 있어서 중요한 원소이다. 본 발명에서는 이러한 Mo를 0.2% 이하로 첨가하는 것이 바람직하며, 보다 바람직하게는, 0.1%이하 범위로 첨가하는 것이다. 만일 Mo의 함량이 0.2%를 초과하면 강판의 경화능이 향상되어 M상 형성에 도움이 되지만, M 함량 자체도 증가하여 항복강도를 증가시키는 현상이 나타날 뿐만 아니라 합금설계 시 원가 상승에도 부적합하다. Molybdenum (Mo) is an element that improves the hardenability in a steel sheet having a composite structure, in particular an important element in forming martensite. In this invention, it is preferable to add such Mo below 0.2%, More preferably, it adds in 0.1% or less range. If the Mo content exceeds 0.2%, the hardenability of the steel sheet is improved to help form the M phase, but the M content itself is also increased to increase the yield strength, and is not suitable for the cost increase in alloy design.
본 발명에서는 Mo와 B을 동시에 첨가하거나, 혹은 Mo를 단독 첨가할 수도 있으며, 이때, 소둔 중 균일한 결정립의 형성으로 성형성 측면에서 유리하게 작용한다. 따라서 본 발명에서는 Mo의 함량을 0.2% 이하로 제한하는 것이 바람직하다.In the present invention, Mo and B may be added at the same time, or Mo may be added alone. In this case, it is advantageous in terms of formability by forming uniform crystal grains during annealing. Therefore, in the present invention, it is preferable to limit the content of Mo to 0.2% or less.
본 발명의 소지강판은 상기 성분 이외에도 잔부 Fe 및 기타 불가피한 불순물을 포함할 수 있다. The steel sheet of the present invention may include the balance Fe and other unavoidable impurities in addition to the above components.
또한 본 발명의 용융아연도금강판 등을 이루는 소지강판은, 경화원소인 Mn 및 Cr의 관계에서 1.3≤Mn(wt%)/(1.15×Cr(wt%))≤20.5의 관계를 유지하는 것이 바람직하다. Mn 대비 Cr 함량이 높아지면 경화능 측면에서는 양 원소의 작용이 유사할지라도 내식성 향상원소인 Cr을 과다하게 첨가하게 되면, 열연 후 산세 스케일 제거에 문제가 있으므로 특히, 외판용 강재에 사용이 불가하다. In addition, the base steel sheet constituting the hot-dip galvanized steel sheet or the like of the present invention preferably maintains the relationship of 1.3≤Mn (wt%) / (1.15 × Cr (wt%)) ≦ 20.5 in the relation between Mn and Cr, which are hardening elements. Do. When Cr content is higher than Mn, even if both elements have similar functions in terms of hardenability, excessive addition of Cr, an element that improves corrosion resistance, is problematic in removing pickling scale after hot rolling. .
따라서 본 발명에서는 소지강판이 1.3≤Mn(wt%)/(1.15×Cr(wt%))≤20.5의 관계를 만족할 것이 소망스럽다. 만일 Mn(wt%)/(1.15×Cr(wt%))의 관계식에서 그 값이 20.5를 초과하면 외판 표면 품질을 확보할 수 없으며, 그 값이 1.3 미만이면 Mn 함량이 상대적으로 높아져 조직 내 Mn-band가 형성되어 표면결함과 더불어 가공불량이 발생할 수 있기 때문이다. Therefore, in the present invention, it is desired that the base steel sheet satisfies the relationship of 1.3 ≦ Mn (wt%) / (1.15 × Cr (wt%)) ≦ 20.5. If the value exceeds 20.5 in the relation of Mn (wt%) / (1.15 × Cr (wt%)), the surface quality of the shell cannot be secured. If the value is less than 1.3, the Mn content becomes relatively high and Mn in the tissue This is because a band is formed and surface defects and processing defects may occur.
또한 본 발명에서 요구되는 C 함량 0.012%이하의 극저탄소강을 이용하여 복합조직강을 제조하기 위해서는, 경화능 향상원소인 Mn, Cr등의 적절 수준 이상의 첨가가 수반되어야 한다. 본 발명에서는 하기 [관계식 1]에 의해 정의되는 마르텐사이트(M)상 형성을 위한 경화능을 나타내는 Mneq값이 1.9≤Mneq≤3.9를 만족하도록 성분 조성을 제어하는 것이 바람직하다. In addition, in order to produce a composite tissue steel using ultra-low carbon steel having a C content of less than 0.012% required by the present invention, addition of an appropriate level or more such as Mn, Cr, etc., which improves the hardenability should be involved. In this invention, it is preferable to control a component composition so that Mneq value which shows the hardenability for martensite (M) phase formation defined by following [Relational formula 1] satisfy | fills 1.9 <= Mneq <3.9.
만일 상기 Mneq 값이 1.9 미만이면 낮은 C 함량으로 인해 소둔 후 급냉을 하더라도 전혀 마르텐사이트(M)상이 형성되지 않아 본 발명에 부합되지 않는다. 그리고 상기 Mneq 값이 3.9를 초과하면 복합조직강은 만들 수 있으나 다량의 합금원소 첨가로 인해 항복강도와 인장강도의 상승이 수반되고 연신율 저하를 가져올 수 있다. 이를 고려하여, 본 발명에서는 상기 Mneq 값이 1.9~3.9 범위가 되도록 관리함이 바람직하며, 보다 바람직하게는 2.1~3.5 범위로 관리하는 것이다. If the Mneq value is less than 1.9, even if quenched after annealing due to the low C content, the martensite (M) phase is not formed at all, which is not in accordance with the present invention. If the Mneq value exceeds 3.9, composite tissue steel may be made, but the addition of a large amount of alloying elements may lead to an increase in yield strength and tensile strength and may cause a decrease in elongation. In consideration of this, in the present invention, it is preferable to manage the Mneq value in the range of 1.9 to 3.9, more preferably in the range of 2.1 to 3.5.
[관계식 1][Relationship 1]
Mneq = Mn + 0.45Si + 2P + 1.15CrMneq = Mn + 0.45Si + 2P + 1.15Cr
한편 상술한 성분조성을 만족하는 본 발명의 용융아연도금강판 내지 합금화 용융아연도금강판은, 그 소지강판의 미세조직으로 주상 페라이트와 잔부 마르텐사이트를 포함하는 것이 바람직하며, 이때 일부 베이나이트를 포함할 수도 있으며, 베이나이트의 량은 가급적 최소화하거나 없는 것이 바람직하다. On the other hand, the hot-dip galvanized steel sheet to the alloyed hot-dip galvanized steel sheet of the present invention that satisfies the above-described component composition, it is preferable to include the columnar ferrite and the balance martensite as a microstructure of the base steel sheet, and may include some bainite The amount of bainite is preferably minimized or absent as much as possible.
따라서 본 발명의 용융아연도금강판을 이루는 소지강판은 그 미세조직이 전 두께(t) 기준으로 면적%로 95% 이상의 페라이트와, 잔부 경질의 제 2상으로 구성됨이 바람직하다. 본 발명에서 상기 페라이트 분율이 95%미만의 경우에는 상대적으로 2상의 분율이 증가하여 복합조직강을 만드는 데는 유리하다. 그러나 페라이트 분율이 작아지면 항복강도 및 항복비가 상승하여 이 역시 부품가공시 표면 굴곡 결함 발생이 높으므로 상기 페라이트 분율을 95%이상으로 함이 바람직하다Therefore, the base steel sheet constituting the hot-dip galvanized steel sheet of the present invention is preferably composed of a microstructure of 95% or more of ferrite and the remaining hard second phase in area% based on the total thickness (t). In the present invention, when the ferrite fraction is less than 95%, it is advantageous to make the composite tissue steel by increasing the fraction of two phases relatively. However, when the ferrite fraction decreases, the yield strength and yield ratio increase, which also causes high surface bending defects during machining. Therefore, the ferrite fraction is preferably 95% or more.
이때 본 발명에서는 상기 경질의 제2상 중에 평균 직경 1㎛이하의 미세 마르텐사이트 분율이 면적%로 2%이하(0%제외)로 됨이 바람직하다. 매우 미세한 마르텐사이트(M) 상이 폭 넓게 분포할수록 마르텐사이트 상 주변에 형성된 가동 전위와 고용 C의 상호 작용에 의해 우수한 소부경화성을 나타낸다. 그런데 상기 제2상 중에 평균 직경 1㎛이하의 미세 마르텐사이트 분율이 면적%로 2%를 초과하게 되면, 항복비가 상승하고 항복강도도 높아져서 가공 시 표면 불량 발생이 높아질 수 있으므로, 상기 마르텐사이트상 분율을 면적비로 2%이하로 관리함이 바람직하다. At this time, in the present invention, it is preferable that the fraction of fine martensite having an average diameter of 1 µm or less in the hard second phase is 2% or less (excluding 0%) in area%. The wider the very fine martensite (M) phase is, the better the bake hardenability is due to the interaction between the movable potential formed around the martensite phase and the solid solution C. However, when the fraction of fine martensite having an average diameter of 1 μm or less in the second phase exceeds 2% as area%, the yield ratio increases and the yield strength also increases, thereby increasing the surface defects during processing. It is desirable to manage the ratio to 2% or less by area ratio.
또한 본 발명에서는 하기 [관계식 2]에 의해 정의되는 면적 %로 페라이트 결정립계에 존재하는 마르텐사이트 점유비율이 90% 이상으로 됨이 바람직하다.In addition, in the present invention, it is preferable that the martensite occupancy ratio present in the ferrite grain boundary is 90% or more at the area% defined by the following [Relational Formula 2].
[관계식 2][Relationship 2]
P(%) = {Pgb/(Pg+Pgb)}×100 P (%) = {Pgb / (Pg + Pgb)} × 100
(여기서, P: 페라이트 결정립계에 존재하는 마르텐사이트 점유율, Pgb: 페라이트 결정립계에 존재하는 마르텐사이트 점유 면적, Pg: 페라이트 결정립내에 존재하는 마르텐사이트 점유 면적을 나타낸다)(Here, P: shows martensite occupancy in the ferrite grain boundary, Pgb: martensite occupancy area in the ferrite grain boundary, Pg: shows the martensite occupancy area in the ferrite grain)
상기 [관계식 2]에서 P(%)가 90% 미만의 경우에는, 페라이트(F) 입내에 형성된 마르텐사이트(M) 상이 많아 내시효성이 우수한 소부경화강을 제조할 수 없기 때문이며, 보다 바람직하게는 92%이상인 것이다. 이는 다시 말해 결정립계에 미세한 마르텐사이트상이 다수 존재할 경우 내시효성이 우수한 소부경화강 제조에 보다 유리함을 알 수 있다. If P (%) is less than 90% in the above [Relation Formula 2], it is because it is impossible to produce a small hardened steel excellent in aging resistance because there are many martensite (M) phases formed in the ferrite (F) mouth, and more preferably, 92% or more. In other words, it can be seen that the presence of a large number of fine martensite phases in the grain boundary is more advantageous for the production of aging hardened steel excellent in aging resistance.
즉, 결정립계에 형성된 마르텐사이트(M)상 주변의 페라이트(F)상에는 다량의 가동 전위가 형성되고 고용 C과의 상호작용에 의해 소부경화성을 나타낸다. 통상의 소부온도(Baking Temperature 170℃, 20분)에서는 마르텐사이트 상에 농축된 C의 활동도가 높아 가열시 페라이트 상으로 확산 이동하여 전위와 상호작용(이하 Locking이라 한다)하여 우수한 소부경화성을 나타낸다. 반면에, 인공시효(100℃, 1시간)의 조건에서는 마르텐사이트 상에 농축된 C의 활동도가 낮아 C이 페라이트(F)상으로 확산 이동치 않고 마르텐사이트(M)상에 그대로 잔존되어 마르텐사이트 상 주변의 전위와의 Locking 되지 않아 시효가 문제되지 않는다. 이러한 측면에서 조직내 마르텐사이트(M)상이 결정립계에 존재할수록 페라이트(F) 상 주변에 많은 가동 전위가 형성되고 내시효 특성이 우수한 소부경화강 제조가 가능하다. In other words, a large amount of movable potential is formed on the ferrite (F) around the martensite (M) phase formed in the grain boundary, and the baking hardness is exhibited by interaction with the solid solution C. At normal baking temperature (Baking Temperature: 170 ℃, 20 minutes), the activity of C concentrated on martensite is high, and it diffuses and moves to ferrite phase when heated to interact with dislocation (hereinafter referred to as 'locking'), showing excellent baking hardening property. . On the other hand, under conditions of artificial aging (100 ° C., 1 hour), the activity of C concentrated on martensite is low, and C remains as it is on martensite (M) without diffusing to ferrite (F). Aging is not a problem because it is not locked with potentials around the site. In this regard, as the martensite (M) phase in the grain is present at the grain boundaries, many movable dislocations are formed around the ferrite (F) phase, and it is possible to manufacture hardened hardened steel having excellent aging characteristics.
한편 본 발명에서는 하기 [관계식 3]에 의해 소지강판 1/4t지점에서 마르텐사이트(M) 상에서의 평균 Mn 농도 wt%(a)와 상기 마르텐사이트(M) 상 주변 1㎛이내 페라이트상에서의 평균 Mn농도 wt%(b)차가 0.3wt% 이상이 되도록 함이 바람직하다. Meanwhile, in the present invention, the average Mn concentration wt% (a) of martensite (M) on the martensite (M) and the average Mn of the ferrite phase within 1 μm around the martensite (M) phase at the 1 / 4t point of the steel sheet according to the following [Equation 3]. It is preferable that the concentration wt% (b) difference is 0.3 wt% or more.
[관계식 3][Relationship 3]
a-b ≥ 0.3wt%a-b ≥ 0.3wt%
(여기서, a는 소지강판 1/4t지점에서 마르텐사이트 상에서의 평균 Mn 농도(wt%), 그리고 b는 상기 마르텐사이트 상 주변 1㎛이내의 페라이트 상에서의 평균 Mn 농도(wt%)를 나타낸다.)(Where a denotes the average Mn concentration (wt%) on martensite at 1 / 4t of the base steel sheet, and b denotes the average Mn concentration (wt%) on ferrite within 1 μm around the martensite phase.)
상기 제 2상의 강도, 즉 마르텐사이트(M)상의 경한 정도가 높을수록 본 발명에 부합되는데, 마르텐사이트상 자체의 강도가 높아 질려면 마르텐사이트상에 포함된 Mn 함량이 주변의 페라이트상 대비 높아야 된다. 이는 마르텐사이트상의 강도가 높을수록 상대적으로 주변의 페라이트상의 연질화가 가능하여 항복강도 및 항복비가 낮은 강판을 제조할 수 있으며 내시효특성이 우수한 소부경화강 제조가 가능하다.The higher the hardness of the second phase, that is, the hardness of the martensite phase (M), the higher the degree of conformity to the present invention. In order to increase the strength of the martensite phase itself, the Mn content contained in the martensite phase must be higher than that of the surrounding ferrite phase. . The higher the strength of the martensite phase, the softer the nitriding of the surrounding ferrite phase is possible, and thus the steel sheet having a lower yield strength and yield ratio can be manufactured, and the hardened hardened steel having excellent aging characteristics can be manufactured.
즉, 마르텐사이트상의 강도가 높을수록 마르텐사이트상 내 고용 C의 농화도(밀집도)가 높아 적정 수준의 소부 온도에서 마르텐사이트상 내 C이 페라이트상으로 쉽게 확산 이동하여 소부경화성을 향상시키기 때문이다. In other words, the higher the strength of the martensite phase, the higher the concentration (density) of the solid solution C in the martensite phase, so that the C in the martensite phase is easily diffused and transferred to the ferrite phase at an appropriate level of baking so as to improve the baking hardness.
이러한 관점에서, 마르텐사이트상과 주변 1㎛이내 페라이트상에서의 Mn 농도 차이(wt%)가 높을수록 유리하다. 만일 상기 Mn 농도차이가 0.3wt% 미만이면, 소부시 C이 쉽게 페라이트상으로 확산 이동치 않아 소부경화성이 열위할 수 있으므로 그 농도차를 0.3wt% 이상으로 관리함이 바람직하다. From this point of view, the higher the difference in Mn concentration (wt%) between the martensite phase and the ferrite phase within 1 μm of the surrounding, the better. If the difference in Mn concentration is less than 0.3 wt%, it is preferable to manage the concentration difference at 0.3 wt% or more since baking C may not be easily diffused into ferrite phase and the baking hardness may be inferior.
한편 상기 각 상(마르텐사이트(M)상 혹은 페라이트(F)상)의 Mn 농도 분석은 TEM을 이용하여 EDS분석기법을 이용하여 각 상에서 10 Point를 측정하여 그 평균값으로 측정하여 행할 수 있다. On the other hand, Mn concentration analysis of each phase (martensite (M) phase or ferrite (F) phase) can be carried out by measuring the average value of 10 points in each phase by using an EDS analysis method using a TEM.
상술한 바와 같은 강 조성성분 및 미세조직을 갖는 본 발명은 항복강도는 조질압연 전에 210MPa이하이고 항복비(YS/TS)는 0.55이하로서 항복강도와 항복비가 낮은 냉연강판, 용융아연도금강판 및 합금화용융아연도금강판을 제공할 수 있다. In the present invention having the steel composition and microstructure as described above, the yield strength is less than 210MPa before the temper rolling and the yield ratio (YS / TS) is 0.55 or less, yield strength and yield ratio cold rolled steel sheet, hot-dip galvanized steel sheet and alloying Hot dip galvanized steel sheet can be provided.
또한 기본적으로 소부경화특성(BH성)은 40MPa 이상 확보가 가능하고, 상온에서 6개월 시효 보증이 가능하도록 인공시효평가(100℃, 1hr)후 인장시험에서 항복점연신(YP-El)이 전혀 나타나지 않는 내시효특성이 우수한 소부경화강을 제공할 수수 있다. In addition, it is possible to secure more than 40MPa of bake hardening property (BH property), and no yield point extension (YP-El) appears in tensile test after artificial aging evaluation (100 ℃, 1hr) to guarantee 6 months aging guarantee at room temperature. It can provide the hardened hardened steel with excellent aging resistance.
다음으로, 본 발명의 내시효성과 우수한 소부경화특성을 갖는 복합조직형 용융아연도금강판 내지 합금화 용융아연도금강판의 제조방법에 대하여 상세히 설명한다. 물론 아연도금을 행하지 않은 냉연강판(소지강판)도 본 발명의 범주에 포함된다. Next, the method for producing a composite-structured hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet having the aging resistance and excellent bake hardening properties of the present invention will be described in detail. Of course, cold-rolled steel sheets (base steel sheets) not galvanized are also included in the scope of the present invention.
먼저, 본 발명에서는 상술한 바와 같은 강 조성성분을 갖는 강 슬라브를 마련한 후, 이를 재가열한다. 이러한 재가열공정은 후속하는 열간압연 공정을 원활히 수행하고, 목표로 하는 강판의 물성을 충분히 얻기 위해 행하여진다. 본 발명은 이러한 재가열 조건에 특별히 제한되지 않으며, 통상의 조건이면 무방하다. 일 예로 1100~1300℃의 온도범위에서 재가열 공정을 수행할 수 있다.First, in the present invention, after preparing a steel slab having a steel composition as described above, it is reheated. This reheating process is performed to perform the following hot rolling process smoothly and to sufficiently obtain the physical properties of the target steel sheet. The present invention is not particularly limited to such reheating conditions, and may be normal conditions. For example, the reheating process may be performed at a temperature range of 1100 to 1300 ° C.
이어, 본 발명에서는 상기 재가열된 강 슬라브를 Ar3+20℃~950℃의 온도범위에서 마무리 열간압연한 후, 450~700℃에서 권취하는 공정을 포함한다.Subsequently, the present invention includes a step of winding the reheated steel slab at a temperature range of Ar 3 + 20 ° C. to 950 ° C., followed by winding at 450 to 700 ° C.
이때, 본 발명에서는 상기 재가열된 강 슬라브를 하기 [관계식 4]에 의해 정의되는 Ar3+20℃~950℃의 온도범위에서 마무리 열간압연하는 것이 바람직하다. 마무리 열간압연의 경우, 근본적으로 오스테나이트계 단상역에서 하는 것이 유리하다. 이는 오스테나이트 단상역에서 마무리 압연을 행함으로써 기본적으로 단상 결정립으로 구성되는 조직에서 보다 균일한 변형을 가하여 조직 내 균일성을 증가시킬 수 있기 때문이다. 만일 마무리 열간압연온도가 Ar3+20℃ 미만이면 페라이트+오스테나이트 2상역 압연 가능성이 높아 재질 불균일성을 가져올 수 있다. 반면에 950℃를 초과하면 고온 압연에 의한 이상 조대립 형성으로 재질불균일에 의한 열연 냉각시 코일 뒤틀림현상이 발생할 수 있다. At this time, in the present invention, it is preferable to finish hot rolling the reheated steel slab in the temperature range of Ar3 +20 ℃ ~ 950 ℃ defined by the following [Relationship 4]. In the case of finishing hot rolling, it is advantageous in the austenitic single phase region essentially. This is because by performing finish rolling in the austenite single phase region, the uniformity in the tissue can be increased by more uniform deformation in the tissue basically composed of single phase grains. If the finish hot rolling temperature is less than Ar3 + 20 ° C, the ferrite + austenite two-phase rolling is likely to be high, which may result in material nonuniformity. On the other hand, if the temperature exceeds 950 ° C, the coil warping may occur during hot rolled cooling due to material unevenness due to the formation of abnormal coarse grains caused by high temperature rolling.
[관계식 4][Relationship 4]
Ar3=910 - 310*C - 80*Mn - 20*Cu - 15*Cr - 55*Ni - 80*Mo Ar3 = 910-310 * C-80 * Mn-20 * Cu-15 * Cr-55 * Ni-80 * Mo
(여기서, Ar3: 이론식 온도)Where Ar3 is the theoretical temperature
그리고 본 발명에서는 상기 마무리 열간압연된 열연판을 450~700℃에서 권취한다. 권취온도가 450℃ 미만이면 과다한 마르텐사이트 또는 베이나이트가 생성되어 열연강판의 과다한 강도 상승을 초래함으로써 후속되는 냉간압연 시 부하로 인한 형상불량 등의 문제가 발생할 우려가 있다. 반면, 권취온도가 700℃를 초과하면 강 중 Mn, B 등 용융아연도금의 젖음성을 저하시키는 원소들에 의한 표면농화가 심해지는 문제가 있다. 따라서 이를 고려하여 권취온도를 450~700℃로 제어함이 바람직하다. 이어, 상기 권취된 열연판은 통상의 조건으로 산세 처리될 수 있다.In the present invention, the finish hot rolled hot rolled plate is wound at 450 ~ 700 ℃. If the coiling temperature is less than 450 ℃ excessive martensite or bainite is generated to cause an excessive increase in strength of the hot rolled steel sheet, there is a fear that problems such as shape defects due to the load during the subsequent cold rolling occurs. On the other hand, if the coiling temperature exceeds 700 ℃, there is a problem that the surface thickening by elements that reduce the wettability of the molten zinc plating, such as Mn, B in the steel. Therefore, in consideration of this, it is preferable to control the winding temperature to 450 ~ 700 ℃. Subsequently, the wound hot rolled sheet may be pickled under normal conditions.
다음으로, 본 발명에서는 상기 권취된 열연강판을 40~80%의 압하율로 냉간압연한다. 상기 냉간압연 시 40~80%의 압하율로 실시함이 바람직한데, 만일 냉간 압하율이 40% 미만이면 목표로 하는 두께를 확보하기 어려울 뿐만 아니라 강판의 형상교정이 어려운 문제가 있으며, 반면 80%를 초과하게 되면 강판 에지(edge)부에서 크랙이 발생할 가능성이 높고, 냉간압연의 부하를 가져오는 문제가 있기 때문이다. Next, in the present invention, the wound hot rolled steel sheet is cold rolled at a reduction ratio of 40 to 80%. When the cold rolling is preferably carried out at a reduction ratio of 40 to 80%, if the cold reduction ratio is less than 40%, it is not only difficult to secure the target thickness, but also difficult to correct the shape of the steel sheet, whereas 80% If it exceeds the crack is likely to occur in the steel sheet (edge), it is because there is a problem that brings the load of cold rolling.
후속하여, 본 발명에서는 760℃~850℃의 온도범위에서 연속 소둔공정을 행한다. 소둔 온도는 기본적으로 2상역 소둔으로서, 2상역소둔 시 페라이트와 오스테나이트 분율에 따라 최종 형성되는 마르텐사이트 함량에 차이가 난다. 소둔 온도가 낮을 경우 오스테나이트 함량은 낮아지나 오스테나이트 내에 C의 농화도는 높아 최종적으로 강도가 높은 마르텐사이트상가 형성되어 소부 시 소부경화 특성이 우수하다. 또한 너무 높은 소둔온도는 현장 제조시 판 형상이 뒤틀림 현상 등이 나타나고 상대적으로 조대한 마르텐사이트상이 형성되어 본 발명에서 요구되는 내시효성이 우수한 소부경화강을 제조할 수 없다. 만일 상기 소둔 온도가 760℃ 미만이면, 너무 낮은 온도로 인장 강도가 오히려 높아져 연신율의 저하를 수반할 뿐만 아니라 오히려 부품가공 시 가공크랙 발생 가능성이 높아질 수 있다. 반면에 상기 온도가 850℃를 초과하면, 고온 소둔에 의한 판 형상 불량이 초래되고 소부경화 특성이 잘 나타나지 않는다. 따라서 본 발명에서는 상기 연속 소둔온도 범위를 760℃~850℃로 제한함이 바람직하며, 보다 바람직하게는 770℃~810℃의 범위로 제한하는 것이다. Subsequently, in this invention, a continuous annealing process is performed in the temperature range of 760 degreeC-850 degreeC. The annealing temperature is basically a two-phase annealing, which differs in the final martensite content depending on the ferrite and austenite fractions in the two-phase annealing. When the annealing temperature is low, the austenite content is low, but the concentration of C in the austenite is high. Finally, a high strength martensite phase is formed, so that the bake hardening characteristic is excellent during baking. In addition, the annealing temperature is too high, the plate shape during the field production, such as the appearance of warpage and relatively coarse martensite phase is formed, it is impossible to produce the hardened hardened steel excellent in the aging resistance required in the present invention. If the annealing temperature is less than 760 ° C., the tensile strength is increased to a temperature that is too low, not only to lower the elongation, but also to increase the possibility of processing cracks during machining of parts. On the other hand, when the temperature exceeds 850 ° C., plate-like defects are caused by high temperature annealing, and baking hardening characteristics are hardly shown. Therefore, in the present invention, the continuous annealing temperature range is preferably limited to 760 ° C to 850 ° C, and more preferably to 770 ° C to 810 ° C.
본 온도구간은 전부 2상역(페라이트+오스테나이트) 온도구간이지만, 가능한 한 페라이트 영역이 많이 포함된 온도에서 실행함이 바람직하다. 2상역 소둔 온도에서 초기 페라이트가 많을수록 소둔 후에 결정립성장이 보다 용이하여 연성이 우수해 진다. 또한 오스테나이트 내 C 농화도가 증가하여 마르텐사이트 개시온도(Ms)를 낮춤으로써 후속하는 도금욕에서의 용융아연도금처리 후 최종 냉각시에 마르텐사이트의 형성을 가능하게 하고, 이에 따라 미세하고 균일한 마르텐사이트가 결정립에 많이 분포함으로써 연성 및 저항복비가 우수한 강판을 제조할 수 있다. Although all of these temperature ranges are two-phase (ferrite + austenite) temperature ranges, it is preferable to carry out at a temperature including as much of the ferrite region as possible. The more the initial ferrite at the two-phase annealing temperature, the easier the grain growth after annealing and the better the ductility. In addition, the C concentration in austenite is increased to lower the martensite initiation temperature (Ms), thereby enabling the formation of martensite at final cooling after hot dip galvanizing in a subsequent plating bath, thereby providing a fine and uniform Since martensite is widely distributed in crystal grains, it is possible to produce a steel sheet having excellent ductility and resistance ratio.
그리고 본 발명에서는 상기 연속 소둔된 강판을 630~670℃의 온도범위까지 3℃/s 이상의 평균 냉각속도로 1차 냉각한다. 상기 1차 냉각온도 구간인 630~670℃는 통상 페라이트 또는 퍼얼라이트(이하, "P" 상이라 한다)가 형성되는 온도 구간이다. 다만 이 온도범위에서 냉각속도를 제어함으로써 가능한 한 퍼얼라이트가 형성되지 않도록 하고, 냉각 중에 오스테나이트상으로 C을 최대한 확산시켜 오스테나이트상 내에 C 농화도를 증가시키는 것이 바람직하기 때문이다. In the present invention, the continuous annealing steel sheet is first cooled to an average cooling rate of 3 ° C./s or more to a temperature range of 630 to 670 ° C. The primary cooling temperature section 630 ~ 670 ℃ is a temperature section in which ferrite or pearlite (hereinafter referred to as "P" phase) is usually formed. However, it is because it is desirable to control the cooling rate in this temperature range so that the pearlite is not formed as much as possible, and the concentration of C in the austenite phase is increased by diffusing C into the austenite phase as much as possible during cooling.
즉, 1차 냉각중에 마르텐사이트(M)상 형성 전에 퍼얼라이트(P)상이 형성되면, 항복강도가 상승하고 연신율 저하를 수반하기 때문에 가능한 한 퍼얼라이트상 형성을 억제할 필요가 있다. 이를 위해 냉각속도가 빠를수록 유리하지만 현장 제조 특성상 무조건 냉각속도를 빠르게 할 수 없으므로 그 상한은 제한하지는 않지만 그 냉각속도가 3℃/s 미만의 경우에는 퍼얼라이트상이 형성될 수 있으므로 항복비가 높아져 본 발명에 부합되질 않는다. That is, when the pearlite (P) phase is formed before the martensite (M) phase is formed during the primary cooling, the yield strength is increased and the elongation is lowered. Therefore, it is necessary to suppress the formation of the pearlite phase as much as possible. To this end, the faster the cooling rate is advantageous, but the upper limit is not limited because the cooling rate can not be unconditionally faster due to the manufacturing characteristics of the field, but when the cooling rate is less than 3 ℃ / s, the yield ratio is higher because the yield phase can be formed Does not meet
본 발명에서는 상기 1차 냉각속도를 가능한 한 빠르게 함으로써 도금욕 침지 전에 마르텐사이트상으로의 변태를 최소화하고 최종 2차 냉각시 미세한 마르텐사이트 상을 형성시키는 것이 바람직하다. 1차 냉각중에 미량이나마 탄소(C)가 오스테나이트계로 확산할 수 있는 충분한 시간을 줄 수 있는데, 이는 2 상역에서의 탄소는 항상 유동적으로 통상 탄소(C) 농화도가 높은 오스테나이트계로 탄소는 확산 이동하는데, 온도가 높을수록 시간이 많을수록 그 확산 속도는 증가하게 된다. 따라서 상기 1차 냉각온도는 중요한데, 630℃ 미만이면 너무 낮은 온도로 탄소(C)의 확산 활동도가 낮아 충분히 오스테나이트계로 확산되지 못하여 페라이트 내 탄소(C)농도가 높아 연성확보에 불리하다. 또한 670℃를 초과하면 상기 언급한 특성 측면에서는 유리하지만, 후속하는 냉각공정에서 너무 급냉이 필요하다는 문제가 발생할 수 있다. In the present invention, it is preferable to minimize the transformation to the martensite phase before the plating bath immersion by forming the primary cooling rate as fast as possible and to form a fine martensite phase during the final secondary cooling. During primary cooling, a small amount of carbon (C) can give sufficient time for the austenite to diffuse, which means that the carbon in the two phases is always fluid, and the carbon diffuses into the austenitic system with high carbon concentration. The higher the temperature, the greater the time the diffusion rate increases. Therefore, the primary cooling temperature is important, if the temperature is less than 630 ℃ too low carbon (C) diffusion activity is not sufficiently diffused to the austenite system, the concentration of carbon (C) in the ferrite is disadvantageous to ensure ductility. It is also advantageous in terms of the above mentioned properties to exceed 670 ° C., but the problem may arise that too quenching is necessary in subsequent cooling processes.
이후, 본 발명에서는 상기 1차 냉각된 냉연강판을 아연 도금욕에 침지하여 아연도금을 행하고, 이어, Ms-200℃ 이하의 온도까지 4℃/s 이상의 평균 2차 냉각속도로 냉각하며, 이에 의해 내시효특성 및 소부경화성이 우수한 용융아연도금강판을 제조할 수 있다. 한편 이때 Ms는 하기 [관계식 5]로 정의될 수 있다.Subsequently, in the present invention, the cold-rolled cold rolled steel sheet is immersed in a zinc plating bath to perform zinc plating, and then cooled to an average secondary cooling rate of 4 ° C./s or more to a temperature of Ms-200 ° C. or lower, thereby. It is possible to produce a hot-dip galvanized steel sheet excellent in aging resistance and baking hardening. Meanwhile, Ms may be defined by the following [Relationship 5].
[관계식 5][Relationship 5]
Ms(℃) = 539-423C-30.4Mn-12.1Cr-17.7Ni-7.5MoMs (° C) = 539-423C-30.4Mn-12.1Cr-17.7Ni-7.5Mo
(여기서, Ms: 마르텐사이트 생성 이론식 온도)Where M s is the martensite production temperature
본 연구에 의하면 통상의 용융아연 도금욕조 온도범위인 440~480℃ 통과 전에 마르텐사이트상이 생성하면 최종적으로 마르텐사이트상이 조대화 되는 경향이 있어 저항복비를 얻을 수 없다. 따라서 본 발명에서는 Ms-200℃이하의 조건에서 행함이 바람직한데, 이 이상의 온도에서는 마르텐사이트(M)상의 강도가 낮아 우수한 소부경화성을 나타내지 않기 때문이다. 이때, 냉각속도도 현장 제조 조건이 가능한 4℃/s이상으로 행함이 바람직하다. 물론 상기 2차 냉각속도도 빠를수록 유리하지만 현장 제조 조건을 감안하여 볼 때, 최소한 4℃/s이상의 냉각속도를 유지함으로써 형성된 마르텐사이트(M)상의 강도를 가능한 한 높이는 것이 바람직하다.  According to the present study, if the martensite phase is formed before the passage of the typical hot dip galvanizing bath temperature range of 440 to 480 ° C., the martensite phase tends to coarsen at the end, and thus the resistance ratio cannot be obtained. Therefore, in this invention, it is preferable to carry out on the conditions of Ms-200 degreeC or less, since the intensity | strength of martensite (M) phase is low at this temperature and it does not show the outstanding baking hardening property. At this time, the cooling rate is also preferably performed at 4 ° C / s or more as possible on-site manufacturing conditions. Of course, the faster the secondary cooling rate, the more advantageous, but in view of the field production conditions, it is preferable to increase the strength of the martensite phase formed by maintaining the cooling rate of at least 4 ℃ / s as much as possible.
본 발명에서 상기 용융아연도금처리는 통상적인 온도범위인 440~480℃의 온도역에서의 도금욕(Pot)에 침지함으로써 이루어질 수 있다. 본 발명에서는 이러한 구체적인 용융아연도금처리조건에 제한되는 것은 아니다. In the present invention, the hot dip galvanizing treatment may be performed by immersing in a plating bath (Pot) in the temperature range of the typical temperature range of 440 ~ 480 ℃. The present invention is not limited to these specific hot dip galvanizing conditions.
한편 본 발명에서는 용융아연도금처리를 한후, 합금화를 위하여 460~610℃의 온도역에서 20초 이상 합금화처리를 행하여 합금화 용융아연도금강판을 제조할 수 있다. 이어, Ms-200℃ 이하의 온도까지 4℃/s 이상의 평균 냉각속도로 냉각함으로써 합금화 용융아연도금강판을 제조할 수 있다. 본 발명에서 합금화 온도 범위는 특별히 한정하지는 않지만 통상의 합금화 처리가 용이한 온도 범위를 설정하였다. 다만 상기 합금화 처리온도가 460℃미만의 경우에는 현실적으로 합금화가 불가하며, 610℃를 초과하면 합금화도가 너무 높아 가공시 표면결함을 유발할 수 있다. 또한 그 유지시간도 최소한의 합금화도를 위해 20초 이상이 바람직하며 특별히 합금화도 및 생산성을 고려하여 그 상한은 한정치 않는다. 기타의 조건은 상술한 용융아연도금강판의 경우와 동일하다. Meanwhile, in the present invention, after performing hot dip galvanizing, alloying may be performed for 20 seconds or more at a temperature range of 460 to 610 ° C. to produce an alloyed hot dip galvanized steel sheet. Subsequently, the alloyed hot-dip galvanized steel sheet may be manufactured by cooling at an average cooling rate of 4 ° C./s or more to a temperature of Ms-200 ° C. or less. Although the alloying temperature range in this invention is not specifically limited, The temperature range which the normal alloying process is easy is set. However, when the alloying treatment temperature is less than 460 ℃, it is impossible to realistically alloy, and if it exceeds 610 ℃ alloying degree is too high may cause surface defects during processing. In addition, the holding time is preferably 20 seconds or more for the minimum alloying degree, and the upper limit thereof is not particularly limited in view of alloying degree and productivity. Other conditions are the same as in the case of the hot-dip galvanized steel sheet described above.
이하, 실시예를 통해 본 발명을 보다 상세히 설명한다. Hereinafter, the present invention will be described in more detail with reference to Examples.
(실시예) (Example)
하기 표 1에 나타난 강 조성성분을 강 슬라브를 마련한 후, 하기 표 2와 같은 제조공정을 이용하여 용융아연도금강판 또는 합금화 처리된 합금화 용융아연도금강판을 제조하였다. 하기 표 1에서 발명강 1,2,4,6,8은 용융아연처리(GI) 강판 제조를, 그리고 3,5는 합금화 용융아연강판(GA) 제조를 위해 사용되었다. 그리고 비교강에서는 11, 12강이 GA강판을, 나머지가 GI강판 제조를 위해 사용되었다. After preparing the steel slab of the steel composition shown in Table 1, using a manufacturing process as shown in Table 2 to prepare a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet. In the following Table 1, the invention steels 1,2,4,6,8 were used for the manufacture of hot dip galvanized (GI) steel sheets, and 3,5 were used for producing the alloyed hot dip galvanized steel (GA). In the comparative steels, 11 and 12 steels were used for the GA steel sheet, and the rest were used to manufacture the GI steel sheet.
상기와 같이 제조된 용융아연도금강판들에 대하여 물성 등을 평가하여 하기 표 3에 나타내었다. 이때, 본 발명에서는 조질압연을 행하지 않은 상태에서 항복비가 0.55 이하이고, 소부경화성이 45 MPa이상이며, 그리고 기본적으로 100℃에서 1시간 유지 후 인장시험시 항복점 연신(YP-El)현상이 나타나지 않아 내시효성이 보증되는 것을 목표로 한다.Physical properties of the hot-dip galvanized steel sheets prepared as described above are shown in Table 3 below. At this time, in the present invention, the yield ratio is not more than 0.55, the hardening hardening property is more than 45 MPa, and basically the yield-stretch (YP-El) phenomenon does not appear in the tensile test after maintaining for 1 hour at 100 ° C. It aims at ensuring aging resistance.
이때, 각각의 시험편에 대한 인장시험은 JIS규격을 이용하여 C 방향으로 실시하였으며, 미세조직에서 주상인 페라이트 상을 포함하여 제2상인 마르텐사이트상의 분율은 강판의 판두께 1/4t 지점에서 기지조직을 분석하여 그 결과를 이용하였다. 구체적으로, 마르텐사이트는 우선적으로 광학현미경을 이용하여 Lepelar부식을 통해 면적율을 계산하였으며, 이를 다시 SEM(3000배)을 이용하여 관찰한 후, Count Point 작업을 통해 정확히 측정하여 보정하였다.At this time, the tensile test for each test piece was carried out in the C direction using the JIS standard, the fraction of the martensite phase of the second phase including the ferrite phase as the main phase in the microstructure is known structure at a point of 1 / 4t of the plate thickness of the steel sheet. Was analyzed and the result was used. Specifically, Martensite first calculated the area ratio through Lepelar corrosion using an optical microscope, and observed it again using SEM (3000 times), and then accurately measured and corrected through Count Point operation.
한편, 소지강판 1/4t지점에서 마르텐사이트상에서의 평균 Mn 농도 wt%(a)와 상기 마르텐사이트상 주변 1㎛이내 페라이트상에서의 평균 Mn 농도 wt%(b)는 박막 시편을 제조하여 TEM을 이용하여 Point방식을 이용하여 각 상의 Mn 농도비(wt%)를 10Points이상 측정하여 그 평균을 대표값으로 나타내었다. On the other hand, the average Mn concentration wt% (a) on the martensite phase and the average Mn concentration wt% (b) on the ferrite within 1 μm around the martensite phase at the 1 / 4t point of the steel sheet were fabricated using a TEM. By using the Point method, Mn concentration ratio (wt%) of each phase was measured by 10 Points or more, and the average was represented as a representative value.
시편번호Psalm Number CC MnMn PP SS NN Cr Cr S-Al S-Al B B MoMo MneqMneq Mn/(1.15×Cr)Mn / (1.15 × Cr) 비고 Remarks
1 One 0.0023 0.0023 2.54 2.54 0.011 0.011 0.007 0.007 0.003 0.003 0.52 0.52 0.025 0.025 - - 0.120.12 3.2 3.2 4.2 4.2 발명강 Invention steel
2 2 0.0045 0.0045 2.21 2.21 0.008 0.008 0.005 0.005 0.004 0.004 0.83 0.83 0.032 0.032 - - -- 3.2 3.2 2.3 2.3 발명강 Invention steel
3 3 0.0072 0.0072 2.03 2.03 0.008 0.008 0.006 0.006 0.003 0.003 0.51 0.51 0.033 0.033 0.0008 0.0008 0.030.03 2.6 2.6 3.5 3.5 발명강 Invention steel
4 4 0.0082 0.0082 2.06 2.06 0.091 0.091 0.007 0.007 0.003 0.003 0.34 0.34 0.034 0.034 - - -- 2.6 2.6 5.3 5.3 발명강 Invention steel
5 5 0.0078 0.0078 2.08 2.08 0.013 0.013 0.003 0.003 0.003 0.003 0.68 0.68 0.028 0.028 0.0011 0.0011 -- 2.9 2.9 2.7 2.7 발명강 Invention steel
6 6 0.0093 0.0093 2.08 2.08 0.021 0.021 0.004 0.004 0.004 0.004 0.46 0.46 0.045 0.045 - - 0.050.05 2.7 2.7 3.9 3.9 발명강 Invention steel
7 7 0.011 0.011 1.69 1.69 0.018 0.018 0.005 0.005 0.004 0.004 0.54 0.54 0.053 0.053 - - -- 2.6 2.6 3.0 3.0 발명강 Invention steel
8 8 0.010 0.010 1.92 1.92 0.013 0.013 0.004 0.004 0.005 0.005 0.51 0.51 0.031 0.031 0.006 0.006 0.160.16 2.5 2.5 3.3 3.3 발명강 Invention steel
9 9 0.017 0.017 1.93 1.93 0.011 0.011 0.006 0.006 0.003 0.003 0.35 0.35 0.033 0.033 - - -- 2.4 2.4 4.8 4.8 비교강 Comparative steel
10 10 0.023 0.023 1.75 1.75 0.006 0.006 0.005 0.005 0.003 0.003 0.21 0.21 0.032 0.032 - - -- 2.0 2.0 7.2 7.2 비교강 Comparative steel
11 11 0.033 0.033 1.73 1.73 0.006 0.006 0.004 0.004 0.002 0.002 0.031 0.031 0.041 0.041 - - -- 1.8 1.8 48.5 48.5 비교강 Comparative steel
12 12 0.052 0.052 1.68 1.68 0.007 0.007 0.006 0.006 0.003 0.003 0.028 0.028 0.045 0.045 - - -- 1.7 1.7 52.2 52.2 비교강 Comparative steel
13 13 0.0018 0.0018 0.45 0.45 0.005 0.005 0.007 0.007 0.004 0.004 0.006 0.006 0.036 0.036 - - -- 0.5 0.5 65.2 65.2 비교강 Comparative steel
[관계식 1][Relationship 1]
Mneq = Mn + 0.45Si + 2P + 1.15CrMneq = Mn + 0.45Si + 2P + 1.15Cr
구분 division 열연Hot rolled 냉연 및 소둔Cold rolled and annealed 조직group 비고 Remarks
FDT FDT CT CT 압하율 Rolling reduction 소둔온도 Annealing Temperature 1차 냉각 ℃/s Primary Cooling ℃ / s 합금화 처리유무 Alloying Treatment 2차 냉각 ℃/s Secondary cooling ℃ / s ① ① ② ② ③ ③ ④ ④
1 One 1-1 1-1 921 921 574 574 68 68 773 773 3.7 3.7 No No 5.2 5.2 96.4 96.4 1.8 1.8 95.5 95.5 0.82 0.82 발명예 1 Inventive Example 1
1-2 1-2 918 918 568 568 68 68 745 745 3.6 3.6 No No 6.2 6.2 95.1 95.1 3.2 3.2 92 92 0.28 0.28 비교예 1 Comparative Example 1
2 2 2-1 2-1 923 923 558 558 69 69 795 795 1.5 1.5 No No 4.8 4.8 89.3 89.3 3.3 3.3 89 89 0.18 0.18 비교예 2 Comparative Example 2
2-2 2-2 931 931 586 586 71 71 796 796 4.2 4.2 No No 4.8 4.8 96.2 96.2 1.7 1.7 92 92 0.78 0.78 발명예 2Inventive Example 2
3 3 3-1 3-1 918 918 630 630 75 75 789 789 3.9 3.9 YES YES 4.7 4.7 96.7 96.7 1.61 1.61 92 92 0.45 0.45 발명예 3Inventive Example 3
3-2 3-2 915 915 648 648 72 72 805 805 4.1 4.1 YES YES 2.5 2.5 97.5 97.5 0.78 0.78 86 86 0.44 0.44 비교예 3Comparative Example 3
4 4 4-1 4-1 914 914 552 552 69 69 812 812 3.8 3.8 No No 4.9 4.9 96.3 96.3 1.32 1.32 93 93 0.65 0.65 발명예 4Inventive Example 4
4-2 4-2 921 921 435 435 67 67 821 821 3.4 3.4 No No 5.6 5.6 96.2 96.2 1.78 1.78 91 91 0.63 0.63 비교예 4Comparative Example 4
5 5 5-1 5-1 928 928 632 632 69 69 835 835 4.2 4.2 YES YES 4.9 4.9 95.3 95.3 1.92 1.92 94 94 0.89 0.89 발명예 5Inventive Example 5
5-2 5-2 932 932 725 725 72 72 836 836 4.1 4.1 YES YES 4.8 4.8 97.2 97.2 2.18 2.18 93 93 0.18 0.18 비교예 5Comparative Example 5
6 6 6-1 6-1 928 928 630 630 69 69 861 861 3.9 3.9 No No 6.3 6.3 95.8 95.8 3.2 3.2 86 86 0.17 0.17 비교예 6Comparative Example 6
6-2 6-2 918 918 589 589 69 69 797 797 4.2 4.2 No No 6.2 6.2 97.2 97.2 1.48 1.48 93 93 0.35 0.35 발명예 2Inventive Example 2
7 7 7-1 7-1 919 919 586 586 73 73 785 785 3.8 3.8 No No 4.9 4.9 94.8 94.8 1.93 1.93 93 93 0.44 0.44 발명예 6 Inventive Example 6
8 8 8-1 8-1 921 921 652 652 71 71 824 824 3.6 3.6 No No 4.7 4.7 96.2 96.2 1.82 1.82 91 91 0.85 0.85 발명예 7 Inventive Example 7
8-2 8-2 918 918 648 648 78 78 834 834 3.8 3.8 No No 4.2 4.2 96.4 96.4 1.76 1.76 93 93 0.54 0.54 발명예 8 Inventive Example 8
9 9 9-1 9-1 932 932 685 685 77 77 835 835 4.2 4.2 No No 5.3 5.3 88.2 88.2 4.01 4.01 78 78 0.35 0.35 비교예 7 Comparative Example 7
10 10 10-1 10-1 932 932 695 695 76 76 831 831 3.9 3.9 YES YES 5.2 5.2 87.5 87.5 5.34 5.34 76 76 0.45 0.45 비교예 8 Comparative Example 8
11 11 11-1 11-1 928 928 596 596 78 78 778 778 4.1 4.1 YES YES 5.7 5.7 84.5 84.5 4.98 4.98 77 77 0.65 0.65 비교예 9 Comparative Example 9
12 12 12-1 12-1 918 918 638 638 79 79 795 795 3.4 3.4 No No 5.7 5.7 86.1 86.1 3.78 3.78 79 79 0.74 0.74 비교예 10 Comparative Example 10
13 13 13-1 13-1 915 915 678 678 78 78 803 803 3.5 3.5 No No 4.9 4.9 100 100 0 0 0 0 - - 비교예 11 Comparative Example 11
① 페라이트상 면적비(%)① Ferrite phase area ratio (%)
② 평균직경 1㎛이하의 미세 마르텐사이트 면적비(%)② Area of fine martensite area of less than 1㎛ average diameter (%)
③ 면적 %로 페라이트 결정립계에 존재하는 마르텐사이트 점유비율 P(%) = {Pgb/(Pg+Pgb)}×100③ Martensite occupancy in the ferrite grain boundary in area%, P (%) = {Pgb / (Pg + Pgb)} × 100
④ 소지강판 1/4t지점에서 마르텐사이트상에서의 평균 Mn 농도 wt%(a)와, 상기 마르텐사이트상 주변 1㎛이내 페라이트상에서의 평균 Mn 농도 wt% (b)의 차 = ④ difference between the mean Mn concentration wt% (a) on martensite phase and the mean Mn concentration wt% (b) on ferrite phase within 1 μm around the martensite phase at the 1 / 4t point of the steel sheet =
a-b≥ 0.3 wt% a-b≥ 0.3 wt%
구분 division YS(MPa) YS (MPa) TS(MPa) TS (MPa) El(%) El (%) BH 2% pre strain(170℃× 20min)BH 2% pre strain (170 ℃ × 20min) 시효 YP-El(100℃× 1hr) Aging YP-El (100 ℃ × 1hr) YR(YS/TS) YR (YS / TS) 비고 Remarks
1 One 1-1 1-1 189 189 389 389 42 42 52 52 0 0 0.49 0.49 발명예 1 Inventive Example 1
1-2 1-2 224 224 438 438 38 38 32 32 0 0 0.51 0.51 비교예 1 Comparative Example 1
2 2 2-1 2-1 234 234 439 439 37 37 28 28 0 0 0.53 0.53 비교예 2 Comparative Example 2
2-2 2-2 187 187 392 392 42 42 53 53 0 0 0.48 0.48 발명예 2Inventive Example 2
3 3 3-1 3-1 178 178 384 384 42 42 52 52 0 0 0.46 0.46 발명예 3Inventive Example 3
3-2 3-2 201 201 405 405 41 41 23 23 0 0 0.50 0.50 비교예 3Comparative Example 3
4 4 4-1 4-1 192 192 401 401 43 43 50 50 0 0 0.48 0.48 발명예 4Inventive Example 4
4-2 4-2 235 235 441 441 36 36 43 43 0.2 0.2 0.53 0.53 비교예 4Comparative Example 4
5 5 5-1 5-1 196 196 401 401 43 43 48 48 0 0 0.49 0.49 발명예 5Inventive Example 5
5-2 5-2 196 196 398 398 41 41 59 59 0.8 0.8 0.49 0.49 비교예 5Comparative Example 5
6 6 6-1 6-1 222 222 439 439 38 38 35 35 0 0 0.51 0.51 비교예 6Comparative Example 6
6-2 6-2 187 187 389 389 42 42 49 49 0 0 0.48 0.48 발명예 2Inventive Example 2
7 7 7-1 7-1 173 173 374 374 44 44 46 46 0 0 0.46 0.46 발명예 6 Inventive Example 6
8 8 8-1 8-1 192 192 401 401 42 42 52 52 0 0 0.48 0.48 발명예 7 Inventive Example 7
8-2 8-2 187 187 392 392 44 44 53 53 0 0 0.48 0.48 발명예 8 Inventive Example 8
9 9 9-1 9-1 245 245 465 465 34 34 45 45 0 0 0.53 0.53 비교예 7 Comparative Example 7
10 10 10-1 10-1 238 238 451 451 36 36 48 48 0 0 0.53 0.53 비교예 8 Comparative Example 8
11 11 11-1 11-1 251 251 468 468 35 35 53 53 0.4 0.4 0.54 0.54 비교예 9 Comparative Example 9
12 12 12-1 12-1 268 268 485 485 32 32 48 48 0.2 0.2 0.560.56 비교예 10 Comparative Example 10
13 13 13-1 13-1 196 196 351 351 42 42 35 35 0.4 0.4 0.56 0.56 비교예 11 Comparative Example 11
상기 표 1-3에 나타낸 바와 같이, 본 발명의 강 조성성분 및 제조공정 조건을 모두 만족하는 발명예 1~8의 경우, 조질압연 전 항복강도가 210MPa급 이하이며 항복비가 0.55 이하를 나타낸다. 그리고 기본적으로 BH성이 45MPa이상이고, 100℃×1hr 인공시효 후 인장시험시 YP-El 전혀 나타나지 않아 시효성 측면에서도 우수하였다. As shown in Table 1-3, in the case of Inventive Examples 1 to 8, which satisfies both the steel composition components and the manufacturing process conditions of the present invention, the yield strength before temper rolling is 210MPa or less and the yield ratio is 0.55 or less. Basically, the BH property was more than 45MPa, and YP-El did not appear at all in the tensile test after artificial aging at 100 ° C × 1hr.
상기 표 3에는 강판의 미세조직이 면적비로 95% 이상의 페라이트와 잔부 제 2상으로 이루어지고, 면적 %로 페라이트 결정립계에 존재하는 마르텐사이트 점유비율이 90% 이상 포함으로 이루어지고, 아울러, 소지강판 1/4t지점에서 마르텐사이트상에서의 평균 Mn 농도 wt%(a)와 상기 마르텐사이트상 주변 1㎛이내 페라이트상에서의 평균 Mn 농도 wt% (b) 차가 0.3wt% 이상으로 이루어지는 조건에서 기본적으로 본 발명에서 목적으로 하는 재질 물성을 확보할 수 있음을 알 수 있다. In Table 3, the microstructure of the steel sheet is composed of 95% or more of ferrite and the balance of the second phase, and the percentage of martensite present in the ferrite grain boundary in area% is 90% or more. In the present invention, the difference between the average Mn concentration wt% (a) on the martensite phase and the average Mn concentration wt% (b) on the ferrite phase within 1 μm around the martensite phase at a point / 4t is basically 0.3 wt% or more. It can be seen that the target material properties can be secured.
도 1 본 발명의 일실시예에 따른 소지강판 1/4t지점에서 마르텐사이트상에서의 평균 Mn 농도 wt%(a)와 상기 마르텐사이트상 주변 1㎛이내 페라이트상에서의 평균 Mn 농도 wt%(b)의 차이를 보여주는 그래프로서, TEM을 이용하여 Point방식을 이용하여 각 상의 Mn 농도비(wt%)를 10Points이상 측정하여 그 평균을 대표값으로 나타낸 것이다. 1 is a mean Mn concentration wt% (a) on the martensite phase and the average Mn concentration wt% (b) in the ferrite phase within 1㎛ periphery of the martensite phase at the 1 / 4t point of the steel sheet according to an embodiment of the present invention As a graph showing the difference, the Mn concentration ratio (wt%) of each phase was measured by 10 points or more by using the Point method using a TEM, and the average is represented as a representative value.
도 1에 나타난 바와 같이, 소지강판 1/4t지점에서 마르텐사이트상에서의 평균 Mn 농도 wt%(a)와 상기 마르텐사이트상 주변 1㎛ 이내 페라이트상에서의 평균 Mn 농도 wt%(b) 차이가 0.3wt% 이상에서는 본 발명에서 요구되는 내시효성이 우수한 소부경화형 강판을 제조할 수 있음을 알 수 있다. 즉, 마르텐사이트상의 단단한 정도가 높을수록 본 발명에 부합되는데, 마르텐사이트상 자체의 강도가 높아지려면 마르텐사이트상에 포함된 Mn 함량이 주변의 페라이트상 대비 높아야 된다. 마르텐사이트상의 강도가 높을수록 상대적으로 주변의 페라이트상의 연질화가 가능하여 항복강도 및 항복비가 낮은 강판을 제조할 수 있으며, 아울러, 내시효특성이 우수한 소부경화강 제조도 가능해 진다. 이는 마르텐사이트상의 강도가 높을수록 마르텐사이트상 내 고용 C의 농화도(밀집도)가 높아지므로, 적정 수준의 소부 온도에서 마르텐사이트상 내 탄소(C)가 페라이트상으로 쉽게 확산 이동하여 소부경화성을 향상시키기 때문이다. 마르텐사이트상과 상기 마르텐사이트상 주변 1㎛이내 페라이트상에서의 Mn농도 차이(wt%)가 높을수록 유리하다. 그 Mn 농도차이가 0.3wt% 미만의 경우에는 소부 시 탄소(C)가 쉽게 페라이트상으로 확산 이동치 않아 소부경화성이 열위하므로 그 농도차를 0.3wt% 이상으로 관리함이 바람직하다. As shown in FIG. 1, the difference between the average Mn concentration wt% (a) in the martensite phase and the average Mn concentration wt% (b) in the ferrite phase within 1 µm around the martensite phase is 0.3 wt. In more than% it can be seen that it is possible to manufacture a bake hardened steel sheet excellent in aging resistance required by the present invention. In other words, the higher the hardness of the martensite phase is in accordance with the present invention. In order to increase the strength of the martensite phase itself, the Mn content contained in the martensite phase must be higher than that of the surrounding ferrite phase. The higher the strength of the martensite phase, the softer the nitriding of the surrounding ferrite phase can be produced, and thus the steel sheet having a lower yield strength and yield ratio can be manufactured, and also, the hardened hardened steel having excellent aging characteristics can be manufactured. This is because the higher the strength of the martensite phase, the higher the concentration (density) of solid solution C in the martensite phase, so that carbon (C) in the martensite phase is easily diffused and transferred to the ferrite phase at an appropriate baking temperature, thereby improving the curing property of the martensite phase. Because it is. The higher the difference in Mn concentration (wt%) between the martensite phase and the ferrite phase within 1 µm around the martensite phase is advantageous. When the difference in Mn concentration is less than 0.3 wt%, carbon (C) does not easily diffuse into the ferrite phase during baking, and thus the inferior curing property is inferior.
한편 도 2는 본 발명의 일실시예에 따른 소지강판의 1/4t 지점에서의 페라이트상 주변에 마르텐사이트상이 형성되어 있는 TEM 조직사진을 보여주는 그래프로서, 마르텐사이트상 주변에 많은 전위가 형성되어 기지조직 내 존재하는 고용 C와 밀접한 관계로 인해 BH성이 나타나고 있음을 예측할 수 있다.On the other hand, Figure 2 is a graph showing a TEM tissue picture formed with a martensite phase around the ferrite phase at the 1 / 4t point of the steel sheet according to an embodiment of the present invention, many potentials are formed around the martensite phase The close relationship with Employment C in the organization suggests that BH is occurring.
이에 반하여, 강 조성성분은 본 발명범위 내이나 그 제조공정 조건이 본 발명의 범위를 벗어난 비교예 1-6은 평균직경 1㎛ 이하의 미세 마르텐사이트 면적비가 높거나 페라이트상의 면적비가 기본적으로 낮았으며, 이에 따라 본 발명에서 목적하는 우수한 BH성이 확보되지 않거나 일부 시효문제가 발생하였다. On the contrary, the steel composition is within the scope of the present invention, but the manufacturing process conditions outside the scope of the present invention Comparative Example 1-6 has a high ratio of the fine martensite area of less than 1㎛ average diameter or the area ratio of the ferrite phase is basically low. Therefore, the excellent BH properties desired in the present invention are not secured or some aging problems have occurred.
예컨대, 비교예 6의 경우, 소둔온도가 본 발명의 범위를 벗어나 고온소둔을 행하게 되면 1/4t지점에서의 마르텐사이트상에서의 평균 Mn 농도 wt%(a)와 상기 마르텐사이트상 주변 1㎛이내 페라이트상에서의 평균 Mn 농도 wt%(b) 차가 낮아 마르텐사이트상의 강도가 낮기 때문에 요구되는 BH성을 확보할 수 없었다. For example, in the case of Comparative Example 6, when the annealing temperature is subjected to high temperature annealing out of the range of the present invention, the average Mn concentration wt% (a) on the martensite phase at the 1 / 4t point and the ferrite within 1 μm around the martensite phase Since the difference in average Mn concentration wt% (b) in the phase was low, the strength of the martensite phase was low, so that the required BH property could not be secured.
또한 강 조성성분 자체가 본 발명의 범위를 벗어나는 비교예 7-11은 기본적으로 평균직경 1㎛ 이하의 미세 마르텐사이트 면적비가 높았으며, 성분 자체의 특성도 충족되지 않아 본 발명에서 요구되는 특성을 확보할 수 없었다. In addition, Comparative Example 7-11, in which the steel composition itself is out of the scope of the present invention, basically has a high ratio of fine martensite having an average diameter of 1 μm or less, and the characteristics of the component itself are not satisfied, thereby securing the properties required by the present invention. I could not.
또한 비교예 7-10의 경우, C 함량을 높혀 복합조직강을 제조하는 컨셉이나 기본적으로 C함량이 높아 항복강도가 상승하여 본 발명에서 요구되는 조질압연전 210MPa이하의 항복 강도 확보가 불가하다는 문제점을 수반하였다. In addition, in the case of Comparative Example 7-10, the concept of manufacturing a composite tissue steel by increasing the C content, but basically the C content is high, the yield strength is increased, it is not possible to secure the yield strength of less than 210MPa before temper rolling required by the present invention. Accompanied.
한편 비교예 9-11은 [관계식 1]의 Mneq를 만족하지 못하여, 본 발명에서 요구되는 물성을 확보할 수 없었다. 또한 비교예 7-8은 [관계식 1]과 Mn(wt%)/(1.15×Cr(wt%))의 조건이 만족되나 강 중 C 함량이 본 발명범위에서 벗어난 경우로서 이 역시 본 발명에서 요구되는 물성을 확보할 수 없었다.On the other hand, Comparative Example 9-11 did not satisfy the Mneq of [Relationship 1], it could not secure the physical properties required in the present invention. In Comparative Example 7-8, the conditions of [Relationship 1] and Mn (wt%) / (1.15 × Cr (wt%)) are satisfied, but the C content in the steel is outside the scope of the present invention, which is also required by the present invention. Could not secure physical properties.
이상 실시예를 참조하여 설명하였지만, 해당 기술 분야의 숙련된 당업자는 하기의 특허 청구의 범위에 기재된 본 발명의 사상 및 영역으로부터 벗어나지 않는 범위 내에서 본 발명을 다양하게 수정 및 변경시킬 수 있음을 이해할 수 있을 것이다.Although described with reference to the embodiments above, those skilled in the art will understand that the present invention can be variously modified and changed without departing from the spirit and scope of the invention as set forth in the claims below. Could be.

Claims (10)

  1. 소지강판 표면에 용융아연도금층이 형성되어 있는 용융아연도금강판으로서,A hot-dip galvanized steel sheet having a hot-dip galvanized layer formed on the surface of the base steel sheet,
    상기 소지강판은 중량%로, 탄소(C):0.002~0.012%, 망간(Mn):1.6~2.7%, 인(P):0.03% 이하(0%는 제외), 황(S): 0.01% 이하(0%는 제외), 질소(N):0.01% 이하(0%는 제외), 알루미늄(sol.Al): 0.02~0.06%, 크롬(Cr):1.0% 이하(0%는 제외), 잔부 철 및 불가피한 불순물을 포함하여 조성되고, 또한 1.3≤Mn(wt%)/(1.15×Cr(wt%))≤20.5의 관계를 만족하고, 하기 관계식 1에 의해 정의되는 Mneq가 1.9≤Mneq≤3.9를 만족하며, The steel sheet is in weight%, carbon (C): 0.002 ~ 0.012%, manganese (Mn): 1.6 ~ 2.7%, phosphorus (P): 0.03% or less (excluding 0%), sulfur (S): 0.01% Or less (excluding 0%), nitrogen (N): 0.01% or less (excluding 0%), aluminum (sol.Al): 0.02 to 0.06%, chromium (Cr): 1.0% or less (excluding 0%), It is composed of the balance of iron and unavoidable impurities, and satisfies the relationship of 1.3 ≦ Mn (wt%) / (1.15 × Cr (wt%)) ≦ 20.5, and Mneq defined by the following equation 1 is 1.9 ≦ Mneq ≦ Satisfies 3.9,
    그 강 미세조직이 면적비로 95% 이상의 페라이트와 잔부 경질 제 2상으로 이루어지며,The steel microstructure consists of 95% or more of ferrite and the remaining hard second phase by area ratio,
    하기 관계식 2에 의해 정의되는 페라이트 결정립계에 존재하는 마르텐사이트 점유비율이 90% 이상이며, 그리고 Martensite occupancy in the ferrite grain boundary defined by the following relation 2 is 90% or more, and
    하기 관계식 3에 의해 정의되는, 소지강판 1/4t지점에서 마르텐사이트 상에서의 평균 Mn 농도 wt%(a)와 상기 마르텐사이트 상 주변 1㎛이내의 페라이트 상에서의 평균 Mn 농도 wt%(b)의 차가 0.3wt%이상인 것을 특징으로 하는 내시효성 및 소부경화성이 우수한 용융아연도금강판.The difference between the average Mn concentration wt% (a) on martensite and the average Mn concentration wt% (b) on ferrite within 1 µm around the martensite phase, defined by the following equation (3) Hot-dip galvanized steel sheet excellent in aging resistance and baking hardening, characterized in that more than 0.3wt%.
    [관계식 1][Relationship 1]
    Mneq = Mn + 0.45Si + 2P + 1.15CrMneq = Mn + 0.45Si + 2P + 1.15Cr
    [관계식 2][Relationship 2]
    P(%) = {Pgb/(Pg+Pgb)}×100 P (%) = {Pgb / (Pg + Pgb)} × 100
    (여기서, P: 페라이트 결정립계에 존재하는 마르텐사이트 점유율, Pgb: 페라이트 결정립계에 존재하는 마르텐사이트 점유 면적, Pg: 페라이트 결정립내에 존재하는 마르텐사이트 점유 면적을 나타낸다)(Here, P: shows martensite occupancy in the ferrite grain boundary, Pgb: martensite occupancy area in the ferrite grain boundary, Pg: shows the martensite occupancy area in the ferrite grain)
    [관계식 3][Relationship 3]
    a-b ≥ 0.3wt%a-b ≥ 0.3wt%
    (여기서, a는 소지강판 1/4t지점에서 마르텐사이트 상에서의 평균 Mn 농도(wt%), 그리고 b는 상기 마르텐사이트 상 주변 1㎛이내의 페라이트 상에서의 평균 Mn 농도(wt%)를 나타낸다.)(Where a denotes the average Mn concentration (wt%) on martensite at 1 / 4t of the base steel sheet, and b denotes the average Mn concentration (wt%) on ferrite within 1 μm around the martensite phase.)
  2. 제 1항에 있어서, 상기 소지강판은 상기 소지강판은 보론(B):0.003% 이하(0%는 제외) 및 몰리브덴(Mo): 0.2% 이하(0%는 제외) 중에 1종 이상을 추가로 포함하는 내시효성 및 소부경화성이 우수한 용융아연도금강판.According to claim 1, wherein the steel sheet is the steel sheet is boron (B): 0.003% or less (except 0%) and molybdenum (Mo): 0.2% or less (except 0%) additionally at least one Hot-dip galvanized steel sheet with excellent aging resistance and baking hardening resistance.
  3. 제 1항에 있어서, 상기 제 2상을 이루는 마르텐사이트 상 중에서 평균직경 1㎛이하의 미세 마르텐사이트 면적%가 2%이하(0%제외)인 것을 특징으로 하는 내시효성 및 소부경화성이 우수한 용융아연도금강판.The molten zinc having excellent aging resistance and hardening hardenability according to claim 1, wherein the fine martensite area% having an average diameter of 1 µm or less in the martensite phase forming the second phase is 2% or less (excluding 0%). Plated steel sheet.
  4. 제 1항에 있어서, 조질압연 전 항복강도가 210MPa급 이하이며 항복비가 0.55이하인 것을 특징으로 하는 내시효성 및 소부경화성이 우수한 용융아연도금강판.The hot-dip galvanized steel sheet having excellent aging resistance and hardening hardenability according to claim 1, wherein the yield strength before temper rolling is 210 MPa or less and the yield ratio is 0.55 or less.
  5. 제 1항 내지 제 4항에 기재된 용융아연도금강판의 용융아연도금층을 합금화처리함으로써 제조되는 내시효성 및 소부경화성이 우수한 합금화 용융아연도금강판.An alloyed hot dip galvanized steel sheet produced by alloying a hot dip galvanized layer of the hot dip galvanized steel sheet according to claim 1.
  6. 중량%로, 탄소(C):0.002~0.012%, 망간(Mn):1.6~2.7%, 인(P):0.03% 이하(0%는 제외), 황(S): 0.01% 이하(0%는 제외), 질소(N):0.01% 이하(0%는 제외), 알루미늄(sol.Al): 0.02~0.06%, 크롬(Cr):1.0% 이하(0%는 제외), 잔부 철 및 불가피한 불순물을 포함하고, 또한 1.3≤Mn(wt%)/(1.15×Cr(wt%))≤20.5의 관계를 만족하고, 하기 관계식 1에 의해 정의되는 Mneq가 1.9≤Mneq≤3.9를 만족하는 강 슬라브를 마련한 후, 이를 재가열하는 공정;By weight%, Carbon (C): 0.002-0.012%, Manganese (Mn): 1.6-2.7%, Phosphorus (P): 0.03% or less (except 0%), Sulfur (S): 0.01% or less (0% ), Nitrogen (N): 0.01% or less (excluding 0%), aluminum (sol.Al): 0.02 to 0.06%, chromium (Cr): 1.0% or less (excluding 0%), balance iron and inevitable Steel slab containing impurities and satisfying a relationship of 1.3 ≦ Mn (wt%) / (1.15 × Cr (wt%)) ≦ 20.5, and Mneq satisfying 1.9 ≦ Mneq ≦ 3.9 defined by the following Equation 1. After preparing a process, reheating it;
    상기 재가열된 강 슬라브를 Ar3+20℃~950℃의 온도범위에서 마무리 열간압연한 후, 450~700℃에서 권취하는 공정;A step of winding the reheated steel slab at a temperature range of Ar 3 + 20 ° C. to 950 ° C., followed by winding at 450 to 700 ° C .;
    상기 권취된 열연강판을 40~80%의 압하율로 냉간압연하고, 후속하여, 760℃~850℃의 온도범위로 연속 소둔하는 공정; Cold rolling the wound hot rolled steel sheet at a reduction ratio of 40 to 80%, and subsequently performing continuous annealing at a temperature range of 760 ° C to 850 ° C;
    상기 연속소둔된 강판을 630~670℃의 온도범위까지 평균냉각속도 3℃/s 이상으로 1차 냉각한 후, 아연 도금욕에 침지하여 용융아연도금을 행하고, 이어 Ms-200℃ 이하의 온도까지 4℃/s 이상의 평균 냉각속도로 2차 냉각하는 공정;을 포함하는 내시효특성 및 소부경화성이 우수한 용융아연도금강판의 제조방법.The continuous annealed steel sheet was first cooled to an average cooling rate of 3 ° C./s or more to a temperature range of 630 ° C. to 670 ° C., and then immersed in a zinc plating bath to perform hot dip galvanizing, followed by a temperature of Ms-200 ° C. or lower. Secondary cooling at an average cooling rate of 4 ℃ / s or more; Method of producing a hot-dip galvanized steel sheet having excellent aging characteristics and baking hardening resistance.
    [관계식 1][Relationship 1]
    Mneq = Mn + 0.45Si + 2P + 1.15CrMneq = Mn + 0.45Si + 2P + 1.15Cr
  7. 제 6항에 있어서, 상기 강 슬라브는 상기 소지강판은 보론(B):0.003% 이하(0%는 제외) 및 몰리브덴(Mo): 0.2% 이하(0%는 제외) 중에 1종 이상을 추가로 포함하는 내시효성 및 소부경화성이 우수한 용융아연도금강판의 제조방법.The steel slab of claim 6, wherein the base steel sheet further comprises at least one of boron (B): 0.003% or less (excluding 0%) and molybdenum (Mo): 0.2% or less (excluding 0%). A method for producing a hot-dip galvanized steel sheet having excellent aging resistance and baking hardening resistance.
  8. 제 6항에 있어서, 상기 2차 냉각으로 제조되는 용융아연도금강판을 이루는 소지강판은, The base steel sheet of claim 6, wherein the base steel sheet constituting the hot-dip galvanized steel sheet is manufactured by secondary cooling.
    그 강 미세조직이 면적비로 95% 이상의 페라이트와 잔부 경질 제 2상으로 이루어지며,The steel microstructure consists of 95% or more of ferrite and the remaining hard second phase by area ratio,
    하기 관계식 2에 의해 정의되는 페라이트 결정립계에 존재하는 마르텐사이트 점유비율이 90% 이상이며, 그리고 Martensite occupancy in the ferrite grain boundary defined by the following relation 2 is 90% or more, and
    하기 관계식 3에 의해 정의되는, 소지강판 1/4t지점에서 마르텐사이트 상에서의 평균 Mn 농도 wt%(a)와 상기 마르텐사이트 상 주변 1㎛이내의 페라이트 상에서의 평균 Mn 농도 wt%(b)의 차가 0.3wt%이상인 것을 특징으로 하는 내시효성 및 소부경화성이 우수한 용융아연도금강판의 제조방법.[관계식 2]The difference between the average Mn concentration wt% (a) on martensite and the average Mn concentration wt% (b) on ferrite within 1 µm around the martensite phase, defined by the following equation (3) A method of manufacturing a hot-dip galvanized steel sheet excellent in aging resistance and baking hardening, characterized in that more than 0.3wt%.
    P(%) = {Pgb/(Pg+Pgb)}×100 P (%) = {Pgb / (Pg + Pgb)} × 100
    (여기서, P: 페라이트 결정립계에 존재하는 마르텐사이트 점유율, Pgb: 페라이트 결정립계에 존재하는 마르텐사이트 점유 면적, Pg: 페라이트 결정립내에 존재하는 마르텐사이트 점유 면적을 나타낸다)(Here, P: shows martensite occupancy in the ferrite grain boundary, Pgb: martensite occupancy area in the ferrite grain boundary, Pg: shows the martensite occupancy area in the ferrite grain)
    [관계식 3][Relationship 3]
    a-b ≥ 0.3wt%a-b ≥ 0.3wt%
    (여기서, a는 소지강판 1/4t지점에서 마르텐사이트 상에서의 평균 Mn 농도(wt%), 그리고 b는 상기 마르텐사이트 상 주변 1㎛이내의 페라이트 상에서의 평균 Mn 농도(wt%)를 나타낸다.)(Where a denotes the average Mn concentration (wt%) on martensite at 1 / 4t of the base steel sheet, and b denotes the average Mn concentration (wt%) on ferrite within 1 μm around the martensite phase.)
  9. 제 8항에 있어서, 상기 제 2상을 이루는 마르텐사이트 상 중에서 평균직경 1㎛이하의 미세 마르텐사이트 면적%가 2%이하(0%제외)인 것을 특징으로 하는 내시효성 및 소부경화성이 우수한 용융아연도금강판의 제조방법.10. The molten zinc having excellent aging resistance and hardening hardenability according to claim 8, wherein the martensite phase forming the second phase has a fine martensite area percentage of 1 µm or less in average diameter of 2% or less (excluding 0%). Method of manufacturing plated steel sheet.
  10. 제 6항 내지 제9항 중 어느 한 항에 있어서, 상기 1차 냉각 후, 아연 도금욕에 침지하여 용융아연도금을 행하고, 이어 460~610℃의 온도역에서 합금화처리를 행한 후 Ms-200℃ 이하의 온도까지 4℃/s 이상의 평균 냉각속도로 2차 냉각하는 것을 특징으로 하는 내시효특성 및 소부경화성이 우수한 합금화 용융아연도금강판의 제조방법. 10. The method according to any one of claims 6 to 9, wherein after primary cooling, hot dip galvanizing is performed by immersion in a zinc plating bath, followed by alloying treatment at a temperature range of 460 to 610 ° C, followed by Ms-200 ° C. A method for producing an alloyed hot-dip galvanized steel sheet excellent in aging resistance and baking hardening, characterized by secondary cooling at an average cooling rate of 4 ° C / s or more up to the following temperature.
PCT/KR2016/006398 2015-07-24 2016-06-16 Hot-dip galvanized steel sheet and hot-dip galvannealed steel sheet with excellent shelf life and bake hardenability, and method for manufacturing same WO2017018659A1 (en)

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